International Politics (2020) 57:342–370 https://doi.org/10.1057/s41311-020-00224-w ORIGINAL ARTICLE NATO enlargement and US foreign policy: the origins, durability, and impact of an idea Joshua R. Shifrinson1 Published online: 7 March 2020 © Springer Nature Limited 2020 Abstract Since the Cold War, NATO enlargement has moved from a contentious issue in US foreign policy debates to an accepted plank in US strategy. What explains this development—why has support for enlargement become a focal point in US foreign policy? After first reviewing US policy toward NATO enlargement, this article evaluates a range of hypotheses from international relations theory and policy deliberations that might explain the trend. It finds that no one factor explains the United States’ enlargement consensus. Instead, pervasive US support for enlargement reflects the confluence of several international and domestic trends that, collectively, transformed NATO expansion into a lodestone of US foreign relations. Regardless, the development carries a range of consequences for US national security; although enlargement afforded the United States significant oversight of European security and political developments, it came at the cost of increased tensions and diminished flexibility with Russia, allied cheap-riding, and US overextension. Keywords NATO · United States · Grand strategy · Europe · Post-Cold War · Russia Over the course of a quarter century, NATO enlargement went from a topic barely discussed in public by US policymakers, to a central pillar of US engagement in Europe. Although opposed by many in the academy (Gaddis 1998), the emergence of what I term the ‘enlargement consensus’ has been a striking feature of post-Cold War US foreign relations. Immediately after the Cold War, the George H.W. Bush administration spent 2 years quietly exploring the possibility of NATO enlargement internally, yet avoided openly raising the issue for fear of Soviet (and later Russian) opposition, backlash from the United States’ Western European allies, and uncertainties surrounding US public support for the move. Instead, NATO after the Cold War was presented simply as one of several institutions that could contribute * Joshua R. Shifrinson jris@bu.edu 1 Pardee School of Global Studies, Boston University, 121 Bay State Road, Boston, MA 02215, USA Vol:.(1234567890) NATO enlargement and US foreign policy: the origins, durability,… 343 to European security (Bush 1993, 7; Sayle 2019, chap. 10). A quarter century later, however, the trend has reversed. As former undersecretary of state William Burns notes, ‘expansion of NATO membership’ has ‘stayed on autopilot as a matter of U.S. policy’ since the initial push to enlarge (Burns 2019, 413). Indeed, policymakers across the political spectrum now argue that keeping NATO’s ‘door open’ for future members is a key element of the alliance’s mission of crafting ‘a free and peaceful European continent’ (Burns and Lute 2019, 7; Albright 2010, 15). Even the Donald Trump administration—often believed to be critical of transatlantic cooperation—is publicly supportive of the alliance’s continued expansion to Georgia and Ukraine (White House 2017a). Increasingly, an expanded alliance is depicted as ‘the core of an American-led liberal order,’ and threats to NATO enlargement as a challenge to the order itself (New York Times 2018; Miller 2018; Ikenberry 2018; Mearsheimer 2019). What explains this shift? Why has NATO enlargement dominated US strategy discussions vis-à-vis Europe, and what have been the consequences of enlargement for US engagement in post-Cold War Europe? These issues are understudied. To be sure, a large body of work examines the process by which a decision to expand NATO emerged in the 1990s and continued thereafter (Goldgeier 1999; Asmus 2002; Hendrickson and Spohr 2004; Sarotte 2019). Likewise, prominent research traces the evolution of the United States’ post-Cold War grand strategy and assesses its merits and drawbacks (Posen 2014; Brooks and Wohlforth 2016; Brands 2016). Still, despite the significant effort put into expanding NATO since the early 1990s, little work examines why US strategy places such a premium specifically on NATO enlargement, or evaluates the consequences of this conceptual shift for US national security (for a partial exception, see Jervis 1995, 24–26). Answers to these questions matter for both historical inquiry and international relations (IR) theory. On one level, explaining and evaluating a complex historical event such as sustained US backing for NATO enlargement can shed light on the sources of contemporary debates over the future of the US role in European security, as well as highlight linkages between IR theory and diplomatic history (Van Evera 1997, chap. 5; Trachtenberg 2009, chap. 4; Lebow and Risse-Kappen 1995). Equally important, the analysis can inform theory itself. After all, a foundational question in IR theory concerns the relative weights of structural factors (e.g., polarity) and agency (e.g., individual leaders) in influencing foreign policy (Dessler 1989; Saunders 2009). This is particularly true when discussing US policy under unipolarity—the period stretching for roughly a quarter century following the demise of the Soviet Union in the early 1990s, and perhaps continuing today (Wohlforth 1999). As Robert Jervis (2009) argues, unipolarity is the rarest and least-theorized structural condition in world politics (for extensions, see Monteiro 2014). Although there is a natural tendency to theorize about the dynamics of unipolarity using the US experience, there may therefore be particular features of US politics and policy that make the United States’ behavior under unipolarity distinct from how other unipolar powers may act (Jervis 2009, 200–201). Analyzing the drivers and consequences of sustained US support for NATO enlargement during the unipolar era thus pushes researchers to assess the degree to which core elements of US foreign policy can be explained 344 J. R. Shifrinson by structural elements of unipolarity, or require sui generis variables that may not obtain in other cases.1 Put differently, insofar as backing for NATO expansion was among the seminal aspects of the United States’ foreign policy during US unipolarity, explaining the course and results of this trend helps theorize the dynamics of unipolarity writ large. Building on existing historiography and IR theory, this article makes two interrelated arguments. First, NATO enlargement emerged as a central pillar in US strategic debates owing to a perfect storm of systemic and domestic conditions. Consistent with other research on US strategy deliberations, the article finds that unipolarity and the permissive conditions it fostered facilitated the United States’ enlargement fixation. Nevertheless, the transition from unipolarity to NATO enlargement required a particular set of ideological and policymaking practices. In this sense, unipolarity allowed a specific strategic mindset to develop and abetted its continuation, but the content of this mindset stemmed from unique elements of US politics and policy. By extension, a different unipole also might have made overseas assertiveness a tenet of its grand strategy, but might not have turned to (1) a multilateral alliance such as NATO or (2) enlargement to attain this result. Second, the principal consequence of enlargement has been to maximize US influence in Europe at the cost of mounting threats to the United States, cheap-riding by allies, and intra-alliance friction. I return to these themes below. The remainder of this article proceeds in four sections. Following this introduction, I discuss the evolution of US policy vis-à-vis NATO enlargement and solidification of the enlargement consensus. Second, I outline a range of hypotheses that might explain the trend, before evaluating the arguments and synthesizing the results. Third, I identify merits and drawbacks of NATO enlargement for US strategy in Europe. Finally, I conclude with implications for theory, history, and policy. The United States and NATO enlargement: a brief history NATO enlargement emerged soon after the Cold War as a predominant and, in many ways, counterintuitive theme in US foreign policy. Of course, as Timothy Sayle explains in this issue, NATO had expanded during the Cold War itself, incorporating Greece (1952), Turkey (1952), West Germany (1955), and Spain (1982). Still, with the Soviet threat eliminated by the implosion of the Warsaw Pact (1989–1990) and ultimate Soviet collapse (1991), analysts and policymakers wondered in the early 1990s whether NATO itself was soon destined for the dustbin of history (Sloan 2016, 104; Mearsheimer 1990; Waltz 1993, 74–76). This concern was never realized. Within a year of the Berlin Wall’s fall, US policymakers were already debating whether ‘the United States and NATO [should] now signal to the new democracies of Eastern Europe NATO’s readiness to contemplate their future membership’ in the 1 For similar efforts to examine the sources of post–Cold War unipolarity, see Layne (2002), Brooks and Wohlforth (2008), Walt (2009), Posen (2006), and Mastanduno (1997). NATO enlargement and US foreign policy: the origins, durability,… 345 alliance (Shifrinson 2016, 38). By mid-1992, a ‘consensus’ emerged in the higher reaches of the George H.W. Bush administration that—as the National Security Council (NSC) staff explained—‘we do want to open up the Alliance to new members’ (Lowenkron 1992; for discussion, see Shifrinson 2020, 51–52). Indeed, Bush and his team worried that failure to embrace enlargement would create an opportunity for the nascent European Union (EU) to fill the security vacuum in Eastern Europe, raise questions over whether NATO could adapt to post-Cold War security conditions, and so challenge the United States’ post-Cold War influence in and over Europe (Sayle 2019, 232–240). As one high-level report explained in mid-1991, if the United States was to ‘continue to be a European power,’ it needed to ‘examine where NATO is headed in its policies toward Eastern Europe’ (No author, undated [mid-1991]; also Hutchings 1997, 277). Bush’s defeat in the 1992 presidential election temporarily put these initiatives on hold as the subsequent Bill Clinton administration sought its foreign policy footing (Flanagan 2019, 103–108; Asmus 2002, 18–19). By 1993–1994, however, Clinton and his team came around to the same basic policy regarding NATO enlargement. The main shift was in the ostensible rationale. Where Bush’s team emphasized protecting the US role in Europe, the Clinton administration presented NATO enlargement as a way of buttressing democracy and liberalism in former Soviet client states (Chollet and Goldgeier 2008, 117–125), while hedging against a renewed Russian challenge.2 Driving this process were enlargement proponents such as National Security Advisor Anthony Lake and Assistant Secretary of State for European Affairs Richard Holbrooke. Critics of NATO expansion (e.g., Clemens 1997)— including those in the administration—fretted that enlargement would render NATO unmanageable and indefensible, redivide Europe, have little effect on democratic development, and antagonize Russia. In contrast, Lake, Holbrooke, and other expansion advocates believed such concerns were overstated; Russia could be persuaded to embrace NATO, enlargement would help socialize former Communist states into embracing democratic-liberal norms, and adding members would revitalize the organization while giving the United States new partners with whom to shape alliance policy (Asmus 2002, 27–29; Goldgeier 1999, chaps. 2–3; Hill 2018, 109–116). Enlargement, in short, was viewed as an effective way of making NATO relevant to post-Cold War Europe (Chollet and Goldgeier 2008). Playing off Clinton’s personal predispositions, policy entrepreneurs thus succeeded in bypassing, isolating, corralling, or—as in the case of Deputy Secretary of State Strobe Talbott—converting intra-administration skeptics while mobilizing bipartisan support within Congress for expansion. Rather than emphasize the risks of counterbalancing, leash-slipping, and/or an open-ended commitment, the US strategic logic held that NATO enlargement would ultimately be a force for stability. By 1995–1996, the consensus was such that neither sustained Russian opposition to 2 As Secretary of State Madeline Albright testified in 1997, the United States could not ‘dismiss the possibility that Russia could return to the patterns of the past’. Hence, enlarging NATO assisted in ‘closing the avenue to more destructive alternatives’ in Russia’s future. See US Senate 1998, 8. See also Talbott (2019, 412). 346 J. R. Shifrinson expansion, nor ambivalence on the part of European NATO members such as France (Sloan 2016, 120), affected the basic approach; even warnings from US diplomats and scholars that enlargement could imperil East–West relations and required the United States to take on potentially costly new commitments had no effect on the drive to enlarge (Goldgeier 1999, 73–76, 86–88, 99). Instead, the United States successfully pushed its current NATO allies to invite the Czech Republic, Hungary, and Poland to begin accession talks at the July 1997 Madrid Summit (Gallis 1997; Goldgeier 1999, 119). In fact, the expansion drive was such that US policymakers did not even fully consult existing NATO members when selecting the three countries for inclusion (Goldgeier 1999, 121). The net effect was the alliance’s eastward move following the formal admission of the Czech Republic, Hungary, and Poland at NATO’s 1999 Washington Summit. Yet even before the first round of enlargement was complete, US policymakers were contemplating future expansion (Croft 2002, 97–101; Larrabee 1999; Asmus and Nurick 1996). The late 1990s congressional debate over expansion, for instance, saw several senators push for Romanian and/or Slovenian accession; likewise, many of the existing European members of NATO favored admitting a broad set of new countries if NATO expansion had to happen at all (US Senate 1998, 196, 255; Kamp 1998). This translated into a US declaration at Madrid that the United States recognized the need to promote the ‘increasing integration’ of other Eastern European states into the ‘Euro-Atlantic Community,’ followed by a NATO pledge at the 1999 Washington Summit that the alliance would ‘continue to welcome new members’ (NATO 1997, 1999). Embracing this pledge, nine states in Eastern Europe soon agreed to work together toward gaining NATO membership (Moyer 2000). Significantly, both Republican nominee George W. Bush and Democratic nominee Al Gore supported this Eastern European initiative during the 2000 presidential election, giving further momentum to the emerging consensus that NATO enlargement was to continue (Sloan 2010, 115; Hendrickson 2000/2001, 58). In fact, a striking feature of US policy since the early 2000s has been the absence of debate over NATO’s further expansion. As one former diplomat describes, the second round of expansion in the early 2000s was marked by ‘bureaucratic continuity at the working level […] as debates raged at the political level over which [states] should be admitted.’ The issue, in other words, was not whether other states would be admitted but how many (Hill 2018, 200). This push to consider enlargement’s scope rather than its continued merits (or lack thereof) also paralleled consolidation of the view that—as one former member of Clinton’s NSC staff member and a coauthor put it in the early 2000s—NATO enlargement ‘helped the historically factious Europe become a peaceful, united, and democratic continent’ (Daalder and Goldgeier 2006, 108; Daalder 2005, 42). Reflecting the maturation of the enlargement consensus, this period saw NATO admit seven new states in 2004, two new members in 2009, and two more states in 2017–2019, as well as engaging in membership discussions with Bosnia-Herzegovina, Georgia, and Ukraine (Michta 2009; Garcia 2009; Congressional Research Service 2016; Pifer 2019; Cook and Niksic 2018; RadioFreeEurope/RadioLiberty 2019). Domestic political behavior, too, showcases policymakers’ growing tendency to embrace continued expansion automatically. The first round of post-Cold War NATO enlargement and US foreign policy: the origins, durability,… 347 enlargement, for example, saw the Clinton administration undertake extensive efforts to cultivate congressional and popular opinion; subsequent rounds, however, have not seen similar efforts to shape domestic attitudes (Goldgeier 1999, chap. 5; Hendrickson and Spohr 2004, 326–329). The US Senate, meanwhile, voted for the first round of enlargement only after months of debate as well as testimony by dozens of experts, and even then, 19 Senators voted no. (US Senate 1998; Schmitt 1998). In contrast, post-2000 enlargements witnessed far more limited congressional deliberations, including discussions bundled with other Senate business,3 substantially shorter hearings, and near-unanimous votes favoring enlargement (Garcia 2009; Hanna 2017). In fact, even senators who opposed the first round of NATO expansion in the late 1990s signaled their support for subsequent expansion from the early 2000s onward (Hendrickson and Spohr 2004, 328–329). Put simply, US support for NATO enlargement had become rote by the 2000s. Thus, just as George W. Bush could argue in 2002 that ‘enlargement of NATO is good for all who join us’ and that it would ‘encourage the hard work of political and economic and military reform’ that contributed to a peaceful Europe (see also Bush 2004), so could Barack Obama remark in 2014 that NATO was critical to ‘a Europe that is whole and free and at peace’ and remained open to admitting new members (Obama 2014). Nor did this trend end with the Trump administration—the enlargement consensus continues even in an administration whose commitment to NATO writ large is open to debate (Shifrinson 2017b). Tellingly, the administration welcomed Montenegro’s 2017 accession to NATO with a press release affirming both that ‘the NATO Alliance has been central to ensuring peace and security on the European continent’ and that ‘the door to membership in the Euro-Atlantic community of nations remains open’ (White House 2017b). It then followed up by supporting Macedonia’s accession and reaffirming support for Georgian and Ukrainian membership (White House 2019, 2017b; Ruger 2019). To be sure, analysts have reasons to doubt Trump’s personal commitment to the alliance (Friedman 2018; Washington Post 2018; Barnes and Cooper 2019). In response to these doubts, however, many members of the US foreign policy establishment have doubled down on the idea that NATO enlargement remains a central element of US strategy and key to what Robert Kagan terms a liberal international order promoting ‘global peace’ (Kagan 2018; also New York Times 2018; Brands 2019; Stavridis 2019). And, in a departure from his occasional rhetorical broadsides against the alliance, Trump himself has mused on the possibility of expanding NATO to include states in the Middle East (Oprysko 2020)! In short, the 2020s are beginning with sustained interest from much of the US foreign policy community—including the Trump administration—in retaining NATO and its enlargement as a centerpiece in US foreign policy. Ultimately, having emerged as a tentative concept in the immediate aftermath of the Cold War, NATO expansion 3 For example, the 2003 Senate Foreign Relations Committee enlargement discussion coincided with the 2003 invasion of Iraq, leading senators to simultaneously discuss both NATO enlargement and plans for Iraqi reconstruction. See US Senate 2003. On the limited evaluation, compare the range of witnesses and length of testimony in 1998 to the 2008 discussion (US Senate 2008). 348 J. R. Shifrinson has come to occupy a premier place in US strategy. The enlargement consensus dominates the US discussion vis-à-vis European security. Explaining the trend The preceding section begs the question: Why has the enlargement consensus taken hold in Washington and dominated policy discussions? Moreover, what explains the durability of the enlargement concept in US strategy? Few studies expressly evaluate the reason(s) behind the United States’ pervasive and persistent focus on NATO expansion. This absence may be partly the result of methodological limitations, as a full assessment of US support for enlargement requires access to primary sources that are unlikely to be available for decades. Still, in keeping with this special issue’s focus on offering an initial analysis of enlargement’s legacy, it is worth developing and evaluating a series of hypotheses rooted in IR theory, policy debates, and historiography that might be able to account for the enlargement consensus.4 In what follows, therefore, I outline a range of such arguments, use a combination of congruence procedures and process tracing (George and Bennett 2005, chaps. 9–10) to identify what aspects of the phenomenon each argument can and cannot explain, and attempt to synthesize the results. Enlargement as a byproduct of unipolarity First, the United States’ focus on enlargement might be explained as a byproduct of US unipolarity. This argument is suggested by several realist scholars (Posen 2006, 156–157n19; Layne 2009, 148–149; 2002, 163; Waltz 1998), as well as (less charitably) by several Russian critics of NATO (Radin and Reach 2017; Monaghan 2006), and treats NATO expansion as the result of unchecked US power following the Soviet Union’s demise. In effect, absent another superpower to discipline its behavior, the United States could act largely without concern regarding international opposition to its policies—it could pursue nearly any objective it wanted in international affairs (including NATO enlargement) irrespective of others’ interests. In this, it behaved as many other powerful states have done when enjoying a surfeit of power (Mearsheimer 2001). By this logic, the enlargement consensus took root and gained traction as US leaders came to understand—implicitly or explicitly—the United States’ relative advantages after the Cold War. By extension, analysts would expect the consensus to shift only if or when US power was seriously challenged by other highly capable actors. The timing of NATO enlargement suggests that there is something to this proposition. NATO expansion is fundamentally a post-Cold War phenomenon. Despite taking on four new NATO members during the Cold War, US policymakers only focused on enlargement in a sustained and serious manner—more than doubling 4 In this, I use a range of established IR theories to develop potential specific explanations for the enlargement consensus; on this approach, see Van Evera (1997, 40–43). NATO enlargement and US foreign policy: the origins, durability,… 349 the alliance’s membership—after Soviet power unraveled. Conversely, not only was NATO expansion not a core issue in US strategy debates during Cold War bipolarity, but real concerns existed that NATO was unlikely to survive the end of the US–Soviet contest. This intra-case variation lends credence to the idea that shifts in power were central to at least the emergence of the enlargement consensus. Similarly, it is likely no accident that the period of NATO’s most rapid enlargement in the late 1990s and early 2000s coincided with a belief in many policymaking and analytic circles that US dominance was likely to last indefinitely (Krauthammer 2002; Wohlforth 1999; Kagan 2008, 86; Clinton 1999, iii). Without needing to factor in the risk of great power opposition, US policymakers could attempt to shape European security in whatever fashion the United States deemed attractive—in this case, via NATO expansion. Conversely, had the United States not enjoyed a unipolar era and been forced to contend with a peer competitor from the 1990s onward, then NATO enlargement would likely not have occurred in either the form or fashion it did.5 Even if Eastern European states had the wherewithal to seek entry to the alliance, competition with a peer would likely have compelled the United States to differently weigh the costs and benefits of doing so. At minimum, US analysts would have been compelled to consider whether taking on additional security commitments in the face of a peer challenger was a net gain, given that the commitments might entail risks, and that the resources involved might be needed elsewhere. At maximum, sustained opposition from another great power might have made expansion an unattractive proposition. The emergence of the enlargement consensus might have been unlikely in such circumstances. That said, unipolarity cannot provide a complete explanation for the enlargement consensus. Unipolarity is a structural condition, liberating the unipole from fixing on the concerns of other great powers. Within this, the unipole can embrace a range of objectives. Although expanding its influence and/or attempting to lock in its preferred institutional arrangements may be likely, there is nothing automatic about the result. It is therefore a bridge too far to link US unipolarity per se with NATO expansion. At least in theory, the United States could have kept NATO within its immediate post-Cold War borders and offered bilateral or informal security commitments to Eastern Europe;6 crafted a new security system, as many Soviet and some Western European leaders desired (Sarotte 2009); or pulled up the ramparts and withdrawn from the continent (Gholz et al. 1997, 17–18). Freed of great power constraints, the United States could have embraced any of these options or oscillated between them. That it did not, and that US policymakers instead chose to expand the US presence on the continent via NATO enlargement, indicates that the explanation lies elsewhere. 5 Many opponents of NATO expansion expected that (1) new great powers might soon emerge—suggesting that expansion was strategically risky—just as (2) enlargement might encourage states to counterbalance. See Waltz (1993). 6 NATO’s Partnership for Peace—developed early in the Clinton administration as a way of engaging Eastern European states without formally enlarging NATO—might have offered a mechanism for such commitments. See Art (1998, 400n32) and Walker (2019). 350 J. R. Shifrinson Expansion as power maximization NATO expansion is sometimes presented as an exercise in US power maximization. According to this argument, unipolarity did not fix US interest in NATO expansion. Instead, it took a particular desire to reify US advantages within a unipolar world to foster the enlargement consensus (Posen 2014, xi, 164–165; Walt 2009, 100; Layne 2006, 111–112; Wohlforth 2016, 248–249; Mearsheimer 2014, 78–80). By this logic, a consensus favoring NATO enlargement emerged and solidified as part of what other analysts call a grand strategy of ‘primacy’—reinforcing and sustaining the United States’ post-Cold War dominance by preventing the emergence of other great powers (Posen 2007). NATO was useful in this task as both a platform for sustaining US power projection into Europe via an institution dominated by the United States, and as a venue for expanding the US reach on the continent. In particular, an expanded NATO helped deprive potential Western European competitors of oxygen in crafting an alternative security system to NATO that might undercut US influence, and limited Russian opportunities for reconstituting the former Soviet empire (Shifrinson 2020; Sayle 2019, chap. 10). Ultimately, the more US policymakers fixed on sustaining US dominance, the more valuable NATO and its enlargement became.7 As with the unipolar argument, there is evidence to support this explanation. For one thing, US policymakers often spoke in terms consistent with a basic power maximization story. As early as 1990, for instance, members of the US State Department underscored that NATO could help ‘organize’ Eastern Europe in ways conducive to US interests (Shifrinson 2016, 37), just as other officials underlined throughout 1991–1992 that enlargement was needed to keep NATO relevant in the face of European integration efforts (Vesser 1992; also Art 1996, 9–27). Likewise, US strategists beginning in the mid-1990s discussed enlargement as a way of spreading democracy and free-market economics deemed valuable to US influence while hedging against a Russian attempt to expand its control into Eastern Europe (Reiter 2001, esp. 41–56; Lake 2004, 27–28). By the mid-2000s, this view had morphed into an argument that NATO enlargement abetted power projection even beyond Europe—a key task to achieve primacy—by providing the United States with an operational springboard from which to go abroad, and allowing the United States to mobilize allied will and capabilities in service of this task (e.g., Brzezinski 2003, 15–16, 30). Meanwhile, US policymakers starting in the 2010s framed enlargement as a way of countering a Russian challenge to Europe’s post-Cold War borders (Bandow 2014; Clinton 2010). Additional evidence comes from the manner in which enlargement occurred. In pushing NATO expansion, US strategists not only increased the United States’ reach in Europe, but also tried to use the process to undercut prospective challengers. The firmest evidence for this comes from the interaction between NATO and various 7 This dynamic may have created a related problem. Having decided to suppress alternatives, the United States exposed itself to a form of entrapment whereby hints that states were considering security structures besides NATO could spur enlargement; in effect, the United States reduced its control over events. NATO enlargement and US foreign policy: the origins, durability,… 351 alternative security structures. The initial US decision to explore NATO enlargement soon after the Cold War only emerged as US officials felt pressured to block (1) Soviet/Russian initiatives to transform the Commission on Security and Cooperation in Europe into a security institution competing with NATO, and (2) Western European efforts to craft a security system based on the nascent European Union (Shifrinson 2020; Sayle 2019, chap. 10). Before these respective initiatives seemed to challenge US power and influence on the continent, enlargement had garnered limited US interest. Once they emerged, however, US officials quickly moved to ensure that NATO filled the security vacuum in Eastern Europe. Later US officials then leveraged NATO’s post-Cold War preeminence to continue hindering alternative security arrangements from gaining traction. Thus, faced in the late 1990s with an EU demand that an enlarged NATO make room for European security integration, US policymakers agreed only on the condition that there be no ‘de-coupling’ of European security initiatives from NATO, no ‘duplicating’ of existing NATO strengths, and no ‘discriminating’ against non-EU members (Hunter 2002, chap. 6; Burns 2003, 54–56). Not coincidentally, a major subset of US policymakers then saw as a virtue NATO allies’ growing dependence on US military power, complementarity to US forces, and inability to independently conduct high-end military operations (Van Hooft, this issue). This approach protected NATO prerogatives and US oversight over European security affairs. Confronted, too, with Russian opposition to NATO expansion and claims that the United States used its influence without regard for Russian interests, US policymakers responded by agreeing to consult with Russian officials but expressly refused to halt enlargement (Hill 2018, 114–137, 168–169). Although these steps do not provide dispositive evidence that the enlargement consensus resulted from a US emphasis on power maximization, they suggest a strong linkage. A final piece of circumstantial evidence comes from the fact that NATO enlargement correlated with the solidification of a post-Cold War strategic approach favoring some form of US dominance in Europe. Whether in the form of liberal hegemony, militant primacy, or deep engagement, one of the striking features of post-Cold War US grand strategy is the presence of a bipartisan coalition embracing an expansive US footprint in international affairs overall and in Europe in particular (Porter 2018). To be sure, not all of these approaches operate in the same manner. Nevertheless, post-Cold War US policymakers as a group focused on sustaining the United States’ strategic preeminence. It follows, therefore, that support for NATO enlargement—as the premier tool of US power projection into what was long the wealthiest and most militarily potent area of the world—may have fit neatly into such an agenda. Still, like unipolarity, power maximization does not offer a complete explanation for the NATO enlargement consensus. If power maximization were the major driver, one would expect the enlargement consensus to also dictate an end to expansion when (1) the costs to US power exceeded the benefits, or (2) when there was little more to be gained in denying Russia and/or the EU opportunities to expand. By this logic, one might be able to explain NATO’s incorporation of countries such as the Czech Republic, Hungary, Poland, and Romania as a way of keeping states offering some strategic value out of others’ orbits, but explaining NATO enlargement 352 J. R. Shifrinson to Southeastern Europe or the Baltic states is significantly harder. These states do little to affect the distribution of power, the viability of competing international institutions, or others’ ability to project influence; several (especially the Baltics) increase the risks of the United States having to fight a major regional conflict under sub-optimal conditions (Shifrinson 2017a, 112–113; Hunzeker and Lanoszka 2015/2016, 17–26; Shlapak and Johnson 2016). Therefore, although some degree of power maximization may have been at play in fostering support for enlargement— particularly early on—the argument has difficulty explaining the continued support for enlargement to militarily and strategically ineffectual actors. Expansion as leadership via prestige and credibility A third argument might treat the enlargement consensus as a result of US prestige and credibility concerns rooted in the desire to demonstrate leadership after the Cold War (Butt 2019; Rovner 2020). Per this approach, enlargement showcased US purpose—it functioned as a litmus test of the United States’ intentions, signaled that it would remain engaged in Europe, and underscored that US policymakers recognized the United States’ role as the victor in the Cold War and world’s only superpower. Moreover, with the alliance moving into Eastern Europe largely at the United States’ behest, NATO expansion could not be stopped without prompting questions regarding the US commitment to Europe (and potentially beyond); to back down from further expansion would raise doubts over the United States’ intentions and its political resolve in engaging Europe, and call into question whatever commitments it still sought to maintain. In this sense, the enlargement consensus could reflect the internalization of a strategic argument treating expansion as the premier test of US will and purpose in European security affairs (Lieber 2012). As with unipolarity and power maximization, there is something to the logic of credibility, prestige, and leadership as drivers of the enlargement consensus. It is certainly true that US policymakers in the early 1990s viewed enlargement as a way of counteracting perceived drift in US grand strategy (Chollett and Goldgeier 2008). Bush and his team, for instance, regularly emphasized to domestic and foreign audiences that the United States was wedded to post-Cold War engagement via NATO (Engel 2017, 280, 305, 350–355; Schake 1998, 379–407). Similarly, work by James Goldgeier, Ronald Asmus, and others highlights that many enlargement proponents on Clinton’s team treated expansion as a way of underscoring the United States’ resolve in structuring post-Cold War European security affairs. Furthermore, both the George W. Bush and Barack Obama administrations highlighted that NATO represented what Bush termed the United States’ commitment to ‘a close and permanent partnership with the nations of Europe,’ within which the United States supported ‘the enlargement of NATO’ because it equally embraced ‘a more united Europe’ (New York Times 2002; White House 2016). The argument also garners circumstantial support from the deliberations over expansion to include Georgia and Ukraine. When broached in the late 2000s, including Georgia and Ukraine in NATO was opposed by many of the United States’ European allies, fearful that doing so would antagonize Russia (Myers 2008). Despite NATO enlargement and US foreign policy: the origins, durability,… 353 this, the United States persistently pushed for a pledge that these states would eventually become NATO members (Rice 2011, 670–675). Concerns with NATO’s credibility and influence were at least a partial driver of this effort. As Bush recalled in his memoirs, ‘The threat from Russia strengthened the case for extending [membership plans] to Georgia and Ukraine. Russia would be less likely to engage in aggression if these countries were on a path into NATO’ (Bush 2010, 431). Nor was Bush alone in this; since 2008, a bevy of think tank and policy analysts have emphasized the desirability of keeping Georgian and Ukrainian membership a possibility lest NATO and US credibility suffer (Japaridze 2014; Daalder and Goldgeier 2008; Tobey 2014; Wilson and Kramer 2018). That said, prestige and credibility factors born of leadership concerns face important limitations. If prestige and credibility drove the enlargement consensus, then one would expect policymakers to be mindful of the need not to expose NATO to failures that might undercut its credibility. As noted, however, the opposite often obtained. In particular, expanding to countries along Russia’s flank and promising future expansion to countries engaged in active disputes with Russia raised the likelihood of crises and confrontations—as Russian officials warned from the early 1990s (Wallander 1999, 159–162)—that could challenge NATO’s willingness to act. That these countries have questionable strategic value, and that the United States embraced political expansion without the concomitant military capabilities to defend these areas (Vershbow 2019, 435), reinforced the problem by undercutting the security foundation on which the United States’ commitment to NATO rests. In short, if credibility and prestige dynamics formed and maintained the enlargement consensus, one would expect a reciprocal focus on avoiding situations that might challenge NATO’s credibility and prestige; that this has not occurred poses problems for the thesis. Enlargement as socialization Fourth, one might explain enlargement by reference to the attitudes, ideas, and experiences—in effect, the socialization—of US elites.8 Though analysts do not quite make the point, this approach would propose that NATO had existed for over four decades before enlargement began, surviving the twists of the Cold War and proving effective in organizing Western Europe against the Soviet bloc. In that time, a narrative grew up around the alliance in many US circles: the world wars ostensibly showed that Europe absent the United States was prone to selfdestruct with exceptionally dangerous geopolitical consequences, whereas Europe with the United States—anchored via NATO—could be kept peaceful and cooperative (Engel 2013). This background left US policymakers enjoying wide familiarity with and enthusiasm for the organization, making NATO a natural focus of attention as the United States sought to chart a course after the Cold War. Furthermore, because such policymakers were in a position to influence the careers 8 For a related argument, see Porter (2018). 354 J. R. Shifrinson and expectations of subsequent generations of officials, Cold War-era support for NATO had a natural pathway into ensuring support for NATO after the Cold War. In essence, policymaker familiarity with and support for NATO during the Cold War generated impetus to keep NATO around after 1991, while also fostering conditions encouraging subsequent officials to share similar ideas. Socialization played some role in crafting the enlargement consensus. Many of the key policymakers pushing NATO enlargement such as James Baker, Madeline Albright, and Tony Lake were dedicated trans-Atlanticists, committed to the idea that US engagement in Europe was intrinsically valuable (Hamilton 2019). After the Cold War, such officials fixed on preserving the alliance, and quickly determined that NATO enlargement would simultaneously give the organization a lease on life and allow it to pacify the areas of Europe newly liberated from Soviet influence as it had the rest of the continent (Goldgeier 1999; Sayle 2019; Zelikow and Rice 2019, chap. 5; Lake 2004, 27–28). Furthermore, the reasons often given for this behavior—that NATO had proven its mettle during the Cold War—reflected less a careful analysis than argument via analogy (Khong 1992) that what had succeeded in times past would work in the future; at root, there is little evidence that policymakers systematically assessed NATO’s ability to address the problems and opportunities present in the post-Cold War world (Goldgeier 1999) as one expects from careful strategic planning. Anecdotal evidence further implies that once NATO enlargement began, incentives for officials to embrace the approach quickly emerged. Skeptics of enlargement, for example, were reportedly isolated, and—as one participant in policy deliberations put it— support for enlargement became a ‘litmus test’ in which one was either ‘with us, or against us’ (Kay 2020). Under such circumstances, individuals seeking to continue rising in their profession were incentivized to embrace the alliance’s expansion. Combined, NATO survival and enlargement became a lodestone in postCold War foreign-policy circles. That said, socialization does a better job explaining enthusiasm for enlargement than explaining the enlargement consensus itself. Even if policymakers favored enlargement because (1) Cold War experience left them interested in preserving NATO and (2) expansion was the key to continued career advancement, expanding NATO still required that policymakers have the opportunity to enlarge the alliance without risking US interests. Policymakers, after all, tend to be experts in balancing tradeoffs, and to enlarge NATO when doing so could harm other US interests—as might occur by antagonizing Russia or roiling European politics—would put the cart before the horse. Under such conditions, careers could be endangered and new approaches to European security affairs required. Even policymakers socialized to believe in NATO and to see enlargement as a way forward first needed an opportunity to expand the alliance at limited cost or risk to the United States, and this opportunity (as noted earlier) was most directly a byproduct of post-Cold War unipolarity. The drawbacks of socialization as an account are therefore the inverse of those of the unipolarity explanation. Although accounting for why US official fixed on NATO after the Cold War, socialization ignores the geopolitical conditions needed for enlargement to appear viable. NATO enlargement and US foreign policy: the origins, durability,… 355 Enlargement as domestic politics A final argument might emphasize the domestic utility of NATO enlargement in generating popular support for continued US internationalism (broadly defined). Here, US policymakers eager to assert the United States’ role in world affairs needed to justify this mission to the American people. Popular support for doing so, however, was not foreordained. Tellingly, the United States had to be dragged into both world wars as the US public was slow to embrace foreign engagement (Thompson 2015), just as US policymakers during the Cold War regularly faced public pressure to reduce or limit foreign commitments (Williams 1985). With the Soviet threat eliminated, it was not unreasonable for US policymakers to worry that similar pressure for disengagement could resurface. Sustained NATO enlargement, on the other hand, might help overcome this possibility. By taking on new commitments in Eastern Europe, presenting the alliance as a democracy-and-liberalism promotion device, and downplaying the military and security obligations involved, policymakers might be able to mobilize public and political opinion for continued foreign activism.9 Moreover, the effort could yield a second-order benefit as, having linked NATO expansion with continued US internationalism, policymakers would be able to label proponents of alternative foreign agendas as isolationists and so link them with one ostensible source of World War Two. Consistent with this argument, policymakers after the Cold War were concerned with the task of ‘justify[ing] national security expenditures and build[ing] support for sustained US engagement overseas’ absent a Soviet threat (Eagleburger 1993). More directly, US strategists presented NATO and its post-Cold War enlargement as a lodestone of US internationalism (Sloan 1995, 217–231). Clinton’s early national security strategies were explicit on this point, arguing that the United States had an important role to play in seizing the ‘great promise’ of the post-Cold War world, presenting NATO as ‘central to that process,’ and arguing that enlargement would ‘expand stability, democracy, prosperity and security cooperation’ to make postCold War possibilities a reality (Clinton 1994, i, 22; 1995, i–ii; Hunter 1999). This logic continued through the 2000s. For example, as two former members of the Clinton administration wrote early in the George W. Bush administration: For all the differences between the foreign policies of the Bush administration and the Clinton administration, policy toward NATO enlargement has been one area of significant continuity. The core of the Clinton strategy was to promote peace and stability on the European continent through the integration of the new Central and Eastern European democracies into a wider Euro-Atlantic community.… A revitalized NATO was an important tool for the maintenance of American engagement and leadership.… President Bush has largely picked up where Clinton left off’. (Steinberg and Gordon 2001) 9 Though the importance of the issue is often overstated, it might also allow them to court ethnic voters in key political districts. See Goldgeier (1999, 100–101). 356 J. R. Shifrinson And as President Obama put it during his final NATO summit in 2016, the United States retained an ‘unwavering commitment … to the security and defense of Europe, to our transatlantic relationship, to our commitment to our common defense’ even as ‘the door to NATO membership remains open’ (White House 2016). Also in line with a domestic mobilization argument, policymakers and pundits opposed to NATO enlargement have frequently been presented as acting contrary to US interests. The starkest example of this trend came in 2017 when Senator John McCain accused Senator Rand Paul of ‘working for Vladimir Putin’ when Paul objected to Montenegro’s admission to NATO (Everett and Hanna 2017). However, the phenomenon was also evident in the 1990s. As Jeremy Rosner—later charged with spearheading the Clinton administration’s campaign to mobilize public and congressional opinion in favor of the first round of enlargement—wrote at the time, ‘America’s allegedly isolationist mood’ was ‘the favorite scapegoat of frustrated internationalists’ seeking NATO expansion (Rosner 1996, 14). Indeed, then-Senator Joe Biden criticized the ‘strong strain of isolationism’ in US political discourse when arguing in favor of NATO expansion in 1997, just as Michael Mandelbaum concurrently noted the widespread claim ‘that if we fail to expand NATO as indicated, we will be guilty of isolationism’ (US Senate 1998, 55, 75). Still, though the domestic political utility of NATO expansion should not be understated, it too is insufficient to explain the enlargement consensus. Like socialization, a domestic mobilization argument confronts a chicken-and-egg problem. Although enlargement was used to frame political debates over the United States’ role in the world, there is still a question about why such a role was seen as valuable and viable in the first place. Narratives and framing devices do not float freely; a policy approach expected to yield strategic disasters is unlikely to be embraced (or embraced for long). Domestic actors’ ability to use NATO enlargement to shape political debates thus related directly to the plausibility that enlargement would benefit the United States. Insofar as foreign policy is intended to chart a state’s course in a competitive international system, the capacity to sell this narrative therefore depended at least as much on strategic conditions such as unipolarity as on domestic factors. Put differently, political leaders certainly used NATO expansion for a domestic purpose, but it took a particular set of international conditions to make the link between US internationalism and enlargement a domestically palatable one in the first place. Integrating the results In sum, none of the preceding explanations wholly accounts for why NATO enlargement gained a prominent perch in post-Cold War US foreign policy discussions and remained fixed despite changing international circumstances. Unipolarity can explain the opportunity for enlargement but not the specific form; power maximization can explain elements of the US approach but not its continuation; a desire for prestige and credibility might account for sustained US interest but not risky US behaviors; socialization might explain policymaker enthusiasm for NATO enlargement but not the opportunity to expand; and domestic politics NATO enlargement and US foreign policy: the origins, durability,… 357 help contextualize the enlargement debate and why policymakers saw enlargement as politically advantageous, but do not necessarily capture the attractiveness or durability of the enlargement idea. What, then, accounts for the enlargement consensus? The enlargement consensus is ultimately best understood as a result of mutually reinforcing domestic and systemic factors. Independently, no one variable pushed the United States to embrace NATO enlargement and make it a focal point of post-Cold War US strategy. Together, however, the factors described above helped make the NATO enlargement consensus a nearly overdetermined feature of US foreign policy. Unipolarity provided the key necessary condition. Faced with few constraints on US power after the Cold War, US officials were free to pursue whatever foreign agenda they deemed appropriate and—crucially—to continue operating in this vein with a substantial margin for strategic error; unipolarity allowed US policy a wide range of choice for a long period of time. Against this backdrop, and with (1) supporters of NATO in key policy positions, (2) many US elites embracing the desirability of crafting a world in which the United States remained the preeminent power, and (3) policymakers seeking to mobilize the US public for international action after the Cold War, the stage was set to expand NATO as a way of reinforcing the United States’ position in Europe. In other words, NATO served as a useful vehicle for US ambitions while overcoming the domestic hurdles to this end. Once begun, enlargement then had no natural end point. With US credibility and prestige invested, US policymakers personally engaged in the enlargement project, and domestic critics of expansion at risk of being labeled isolationists, incentives to rein in enlargement were limited. Moreover, the absence of a geopolitical rival ensured that what opposition to NATO expansion did emerge could be normalized and deflected; for example, pushback from Russia and Western European allies could be ignored as it never involved immediate risks to US power or security, nor (at least prior to the 2014 Ukraine crisis) rose to a level that would reveal an obvious failure of US policy. In short, the enlargement consensus emerged from a particular and potent blend of systemic and situational factors. No one variable created the NATO enlargement consensus, though unipolarity provided a key backstop. Collectively, however, there were few reasons not to turn to NATO enlargement, and many contextual—though contestable—reasons to embrace it. As Patrick Porter (2018) observes in a different context, the enlargement consensus reflects a blend of US power and purpose. Consequences of enlargement: the good, the bad, and the ugly Irrespective of its sources, the United States’ firm backing of enlargement carries a range of consequences for US national security. Others in this special issue highlight the particular consequences for Russia, for the European members of NATO, and for the institution itself. So far as the United States is concerned, however, the consequences of enlargement constitute a mixed bag. 358 J. R. Shifrinson The good On the positive side of the ledger, US backing for enlargement has, first, guaranteed the United States’ role as Europe’s preeminent power since the 1990s. This is a sea-change from Cold War bipolarity, as well as an outcome that one could not have automatically expected after the Cold War. Indeed, the 1990s saw a range of proposals for cutting the US presence in Europe, as well as European and Russian schemes for crafting alternative European security frameworks; it was not obvious that the United States would remain a European power or that it would enjoy a decades-long period as the arbiter of European security (Huntington 1999, 45; Kupchan 1998; Layne 1993; Waltz 1993). That US leaders—individuals skilled in the assessment and exercise of power—feared that a Western European grouping might slowly winnow down US strength suggests the uncertainty of the United States’ post-Cold War dominance (Shifrinson 2020). The United States’ sustained backing for NATO enlargement helped foreclose this possibility, reifying US power in Europe by suppressing alternatives that might challenge the US position. Of course, the benefits of this outcome may be overstated. Power in international relations is not an end in itself—it has to be translated into security and/or other results (Baldwin 2012, 273–274). In light of the downsides identified below, it is possible that US security, economic, and ideological interests would have benefited as much if not more from a different distribution of power. Still, ensuring US dominance may have benefited the United States in a second way by clarifying the regional distribution of power and so minimizing debates over whether regional states would have opportunities to press their security advantages against other local actors. This, in turn, may have reduced whatever chance existed that Europe would return to the internecine geopolitical contests that prevailed in the nineteenth and early twentieth centuries, and witness Britain, France, Germany, Russia, and/ or others (e.g., a more cohesive European Union) jockying for position.10 With the United States as Europe’s dominant power and exercising oversight over regional security, the chance of conflict and competition among Europe’s major powers may have waned.11 Although the necessity of American engagement for the maintenance of European peace may also be overstated, clarifying the European distribution of power via NATO enlargement may thereby have still contributed to the United States’ interest in preventing major geopolitical contests on the continent (Art 1999, 89–92). Third, and related to the preceding, enlargement may have reduced the risk of nuclear proliferation in post-Cold War Europe. Again, whether this is intrinsically an advantage for the United States depends on one’s views of the utility of nuclear weapons in stabilizing or undermining international security; certainly, many 10 On miscalculation of the distribution of power as a source of conflict, see Blainey (1988). For nuanced discussion of the situation in Europe, see Glaser (2010, 213–216). 11 This comes on top of ideational, normative, and institutional factors that many scholars argue independently reduce the risk of European competition and conflict. See Mueller (1989) and Risse-Kappen (1996). NATO enlargement and US foreign policy: the origins, durability,… 359 analysts argue that nuclear proliferation limits US freedom of action and increases the probability that nuclear weapons fall into the hands of hostile actors (Gavin 2015). And here, rumors abounded after the Cold War that states not yet in NATO— and even some (e.g., Germany) that were—might pursue independent nuclear programs to obtain security (Sharp 1993, 29–33). By enlarging the alliance and extending the US nuclear umbrella, US policy reduced the incentive for states to invest in such efforts and so improved US security on the nonproliferation front. Last, enlargement may have helped the United States structure European security affairs in ways that promoted other US interests—for example, the spread of democracy and the growth of free markets. The consequences here should also not be overstated. By the Cold War’s end, democracy and free markets already enjoyed widespread appeal in much of Europe, as highlighted by the policies adopted by Eastern European states following the 1989 revolutions; US backing for NATO enlargement did not cause these phenomena (Gunitsky 2017, chap. 5). Still, US support for NATO’s expansion may have reinforced the international antecedents that allowed these trends to continue. For example, in spurring NATO’s move into former members of the Warsaw Pact, the United States helped craft an Eastern European security framework that limited external pressures (e.g., local security dilemmas) that might have undercut liberalizing reforms. Although NATO enlargement appears to have been neither necessary nor sufficient for democratic and free-market growth after the Cold War, it may have thus worked at the margins to promote non-security US interests and made it easier for the United States to project political influence (Brooks and Wohlforth 2016, 115–118, 171–184). The bad On the other hand, NATO enlargement exposes the United States to a variety of security ills while limiting its ability to respond to these dilemmas. First, ongoing expansion requires the United States to defend several Eastern European states of questionable strategic value, up to and including the use of nuclear weapons. Even if some of the members to which NATO has expanded are useful for denying prospective rivals maneuvering room to prove their mettle (e.g., the European Union) or expanding their geographic reach (e.g., Russia), many of the member states to which the United States offered security guarantees via NATO are of minimal long-term importance. Loss of the Baltic states to Russia, for instance, would do little to shift Europe’s strategic map, while none of NATO’s new Southeastern European members are of use in either reinforcing US power or denying power to others (Shifrinson 2017a, 111). Having taken on the commitment, however, the United States— as NATO’s principal military backer—is now stuck having to try to defend these actors. This is no easy task, especially in the Baltics; local geography is unfavorable, the distances involved make reinforcement difficult, and the proximity to local prospective threats—in this case, Russia—means it is nearly impossible to obtain favorable force ratios. Nevertheless, the United States and other NATO members have tried to engage the problem, committing growing assets along the way (Kuhn 360 J. R. Shifrinson 2018; O’Hanlon and Skaluba 2019; Lanoszka and Hunzeker 2019). The alliance is therefore playing a fraught game. The United States and its partners can certainly try to develop military tools to meet NATO’s expanded commitments, but doing so is expensive, may exacerbate tensions with Russia, stands a real chance of failure, and—insofar as allies are under the US security umbrella—risks the United States putting its own survival on the line by extending US nuclear guarantees in the face of a nuclear-armed opponent.12 In sum, US backing for enlargement has left the United States with a suppurating sore of a strategic commitment, putting it on the firing line in Eastern Europe. Relatedly, NATO enlargement limits US flexibility with Russia. Arguably the premier counterfactual in post-Cold War Europe concerns whether US relations with Russia would have turned so contentious absent NATO enlargement. It is certainly true—as the Marten and Lanoszka articles in this issue highlight—that US–Russian friction was likely inevitable after the 1990s as Russian power recovered from its post-Cold War nadir. Still, the persistent warnings proffered by Russian analysts from the 1990s onward that NATO enlargement was likely to be uniquely harmful to Russian policymakers arguing for cooperation with the West suggests that the US push for expansion exacerbated, reinforced, and/or accelerated problems (Wallander 1999; Talbott 2019). By this logic, the enlargement consensus imposes an opportunity cost on Russian–US relations. Even if expansion was not uniquely responsible for the downturn, the continued emphasis on enlargement limits flexibility in dealing with Russia, hindering the United States’ ability to explore options such as retrenchment, spheres of influence, or buffer zones in Eastern Europe that might potentially dampen bilateral tensions. Put differently, with enlargement enjoying substantial domestic support, linked to broader US power maximization, and taken as a sign of US leadership and credibility, policy options that might ameliorate tensions with Russia are screened out of the policy agenda. Along similar lines, the enlargement consensus may exacerbate the intensity with which the United States reacts to challenges to the (now enlarged) alliance. This is partly a product of US efforts to keep NATO the lodestone of European security affairs, as well as of linking US leadership, prestige, and internationalism with NATO enlargement. Seeking, for instance, to assert US prerogatives and to be seen as opposing Russian pressure, US policymakers have led the charge to keep NATO’s door officially open for Georgia and Ukraine irrespective of the problems this poses for East–West relations (e.g., Congressional Research Service 2019, 15; Cirilli 2014; Myers 2008).13 Likewise, US support for and investment in the Kosovo (1999) and 12 To be sure, the United States is free not to utilize nuclear weapons on behalf of a NATO ally amid a crisis. Still, given the questions this could raise over the United States’ future credibility and the concern US leaders have historically shown over the United States’ willingness to reassure its partners, expansion increases the likelihood US leaders may feel obliged to escalate up to and including nuclear use for NATO’s new members. 13 Of course, it remains unclear if the US and/or other NATO members would expand to Ukraine, Georgia, or additional countries bordering Russia if conflict were ongoing. Still, the United States has stressed it is willing to consider continued expansion and, in any case, leaders in Russia, Ukraine, and beyond may believe we are serious about further enlargement. Thanks go to Robert Jervis for help on this point. NATO enlargement and US foreign policy: the origins, durability,… 361 Libya (2011) air campaigns seems to have been partly motivated by a desire to avoid questions about the US commitment to NATO and its efficacy outside of Cold War borders. For instance, one former US official remarked during the Kosovo campaign that failure to obtain NATO’s ends in Kosovo could reopen ‘the question of why American troops are still in Europe’ (Rodman 1999; also Cottey 2009). In the case of Libya, meanwhile, US policymakers eventually decided that the United States would take the lead in the bombing campaign despite having sought a Europeanled effort—an action difficult to explain if not for concerns over NATO’s credibility (Goldberg 2016; Gates 2014, 520–522). Any one of these behaviors is not necessarily problematic. Nor are they unique to the NATO enlargement era; concerns with preserving a credible US commitment to NATO were a major feature of Cold War debates, for instance. Still, in an era without great power threats to justify and motivate the US interest in European security, concerns with sustaining US credibility loom larger and have pushed the United States to undertake a range of risky behaviors for unclear ends. The United States is reluctant to allow an enlarged NATO to be seen as a failure for fear of the blowback on the post-Cold War organization. This outcome is again hard to explain without a post-Cold War policy consensus mandating that NATO remain a potent force in European security with options for the future. After all, with the United States having sidestepped allied opposition on issues ranging from the Multilateral Force (MLF) to the Intermediate-Range Nuclear Forces (INF) treaty during the Cold War, one would expect it to settle or de-escalate at least some of NATO’s post-Cold War disputes as well. Instead, the United States has proven to be trigger happy and prone to use NATO to escalate confrontations rather than go over NATO’s collective head to defuse crises. Lastly, enlargement encourages allied cheap-riding. This is a byproduct of both structure and strategy. Structurally, alliances tend to experience greater cheap-riding the larger they become and the lower the external threat.14 Having pushed for NATO enlargement after the Cold War, the United States confronts both conditions. Given that the alliance now has upward of 30 members, many of its relatively small states can expect others to pick up the security slack. As importantly, because NATO continues in the absence of a clear threat, its eastward move undercuts the incentive that otherwise capable states such as Britain, France, and Germany have to contribute effective forces. With the better part of a continent between them and Russia, for example, the rationale for assisting against the Russian military threat—which analysts suggest is limited in any case (e.g., Radin et al. 2019)—is low. Likewise, calls for the allies to develop expeditionary forces for NATO out-of-area operations are of questionable attraction owing to the limited military challenge emanating from overseas humanitarian or civil-war contingencies. 14 The canonical statement of the first point is Olson and Zeckhauser 1966. The second point needs elaboration. Alliances tend to wax and wane as states pool resources in response to threats. This is costly and risky domestically—requiring resource mobilization—and internationally—as states rely on one another for their security. For alliances facing limited threats, it is reasonable to expect states to buckpass and underinvest in military forces as much as possible, hoping that their allies will instead bear the burdens of confronting what threats there are. 362 J. R. Shifrinson The United States’ approach to enlargement has reinforced these structural incentives. As noted, the United States pushed for NATO enlargement partly to deflect an EU-based alternative to the United States’ post-Cold War preeminence. In doing so, US policymakers struck an implied deal with the European allies: Western Europe would rely upon NATO (and thus the United States) for European security, and the United States would tolerate a degree of European cheap-riding. This logic, for instance, was central to early post-Cold War efforts to ensure that the EU focused on out-of-area operations while leaving European defense to NATO’s purview (Van Hooft, this issue). Later, this approach was implicit in the US effort to ensure that EU-based security forces neither duplicated nor distracted from NATO functions. If EU members were not to craft an autonomous security apparatus, then reliance on NATO and the structural cheap-riding noted above were the logical corollary. Regardless of its sources, cheap-riding has now reached crisis levels. The oncevaunted German military, for instance, looks to be ineffectual and unable to deploy meaningful forces beyond—and perhaps within—its borders (Karnitschnig 2019; BBC News 2018). Similarly, even allies such as Britain, France, and Italy that have invested in some degree of power projection lack assets relevant to the modern battlefield; tellingly, the United States was compelled to resupply several NATO members with modern munitions during the Libya campaign when allied stocks gave out (DeYoung and Jaffe 2011; Shanker and Schmitt 2011). Meanwhile, European logistics and mobilization rates have atrophied, so much so that it might take several weeks or more for the non-US members of NATO to assemble and begin moving forces to address contingencies on NATO’s flank (Kuhn 2018, 28; Shurkin 2017). Collectively, the European allies seem to have embraced cheap-riding to a degree unforeseen by US policymakers, resulting in efforts by the Obama and Trump administrations to push the European allies to reverse course (Birnbaum 2011; Davis 2018). The net result leaves the United States exposed as the military buck-catcher within the alliance, increasing the prospective burdens that the United States might face in wartime, and requiring the United States to work harder if NATO is to matter for deterrence and reassurance in peacetime. The ugly Finally, these dynamics may carry second-order consequences, with enlargement and the accompanying US policy consensus making it more difficult for the United States to manage the alliance than might otherwise be the case. During the Cold War, transatlantic relations were complicated by a series of crises over burden sharing, military strategy, and relations with the Soviet Union. At such times, US policymakers were compelled to negotiate with their European counterparts, resulting in compromises (e.g., over German rearmament in the 1950s and the Dual Track decision in the 1970s) that shaped the alliance’s course. With NATO’s growth from 16 to nearly 30 members since 1990, however, this process is now substantially more complex. Because NATO operates via consensus, the United States now faces pressures from a broader set of partners, each of which must be brought on board and engaged if the United States is to keep NATO operating in desired form. NATO enlargement and US foreign policy: the origins, durability,… 363 This situation is further exacerbated as the absence of a collective threat to the alliance and the greater geographic sprawl of the organization leave member states with varying interests and threat perceptions. Despite several years of negotiations, for example, the United States faced substantial difficulties obtaining buy-in from all NATO members on whether and—increasingly—how to buttress NATO’s eastern flank (Keil and Arts 2018; Dempsey 2017; Deni 2016; Belkin 2016, 2–3, 12). Similarly, public cajoling, threats of abandonment, and private negotiations have failed to convince all NATO members of the need to strengthen their conventional military capabilities (Burns and Lute 2019, 3–4; Schuessler and Shifrinson 2020). Friction is inherent in any alliance. Still, NATO enlargement has likely exacerbated the management difficulties faced by the United States. Conclusion The preceding analysis carries implications for historiography, theory, and policy. For historiography, the work highlights that scholars need to move beyond trying to understand the drivers of NATO enlargement writ large, and directly grapple with the United States’ post-Cold War fixation on enlargement in particular. These issues are related but analytically distinct. The former bears on why the alliance began moving eastward, whereas the latter engages the underlying drivers of US policy across the post-Cold War era. Doing so, moreover, calls for blending political science concepts and policy discussions with developments in historiographic treatments and access to new primary sources. The above assessment provides an initial synthesis aimed at engaging some of the core issues, but is certainly not intended to be the final word. For IR theory, meanwhile, this article reinforces Jervis’s observation that the dynamics of US unipolarity should not necessarily be taken as the norm for any unipole. Again, unipolarity liberated the United States from the immediate pressure of great-power competition. Sustained US backing for NATO enlargement, however, required that unipolarity be married to a particular theory of how the United States could obtain security for itself after the Cold War, backstopped by political and domestic factors that kept this theory in vogue. Scholars interested in examining the course and conduct of unipolarity as a systemic condition would therefore be wise to take the US experience in Europe with a grain of salt. Even if post-Cold War unipolarity made US expansionism more likely than not, repeated and regular NATO enlargement was not a necessary result. Instead, and like other foreign policy decisions, the United States’ enlargement consensus requires blending systemic conditions with domestic variables. That said, future research might fruitfully abstract from the US experience to consider the conditions under which unipoles act in manners similar to the United States and prioritize security structures developed under different systemic circumstances. US unipolarity saw US elites embrace particular foreign policy behaviors, but the behaviors themselves may be more or less likely for some unipoles than others. As for policy, this project raises questions about the future of US engagement in Europe. On one level, showing that the United States’ backing for NATO 364 J. R. Shifrinson enlargement relied upon a set of interlocking domestic and international variables highlights that a course adjustment may be more difficult than proponents of alternate approaches for US grand strategy may expect. Critics of the United States’ existing grand strategy suggest that shifts in the international distribution of power and/or adjusting the ends sought by the United States in world politics may be sufficient to reorient US foreign policy (Posen 2014; Mearsheimer and Walt 2016). If, however, US interest in NATO enlargement stems from both domestic and international factors, then these arguments may not go far enough; it may take not only an end to US unipolarity or power-maximizing tendencies but also the creation of a domestic consensus and political establishment committed to a new course to fully move the United States back from continued NATO enlargement. Absent such a seachange internationally, strategically, and domestically, continued NATO expansion is likely to generate extended debate. In other words, at a moment when US power and purpose in the world are hotly debated, the preceding discussion raises the possibility that discord vis-à-vis NATO may be the new normal. At the same time, the above analysis should give both critics and proponents of enlargement pause in advocating for their respective positions. As highlighted earlier, it is too much to claim that enlargement has been wholly positive or wholly negative so far as US national security is concerned. Rather, enlargement yielded a mixed bag for the United States, helping it dominate Europe but also imposing large direct and indirect costs. Before recommending either more enlargement or a new course, further research is needed on the range of merits and drawbacks of such moves and how these effects compare with the status quo. The NATO enlargement consensus may ultimately change, but policymakers would do well to avoid fixing on a new consensus too soon—judicious appraisal of the potential roads to be taken is needed. Acknowledgements The author gratefully acknowledges the Charles Koch Foundation’s support in sponsoring Boston University’s ‘Evaluating the Legacy of NATO Enlargement’ workshop in May 2019, for which this article was composed. 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