allies. As president, his approach to alliance management softened little. He pointedly refused to endorse Article V of the Washington Treaty (also known as the North Atlantic Treaty) – which provides that an attack on one NATO member is an attack against all – when given the opportunity to do so. He launched trade wars with European allies and Japan, and threatened major economic sanctions while renegotiating free trade agreements with Canada and South Korea – all of which were longstanding US allies. He repeatedly lambasted NATO members for not paying their fair share. His administration had demanded extortionary amounts of money from South Korea in talks over the status and financing of US bases in that country. His desire to strike deals with Russia and North Korea unsettled allies located on their frontiers, fueling concern that a grand bargain would be made at their expense.
It would thus be tempting to conclude that, given Trump’s presidency, the end of US military alliances had seemed imminent. Perhaps that really would have been the case had he won re-election in 2020. We will never know. And yet the record of the previous decade suggests an alternative assessment: many of the seemingly intractable problems that abound in alliance management today have appeared before. It is safe to say that they will persist into the future, even if Trumpism is – possibly – in the rearview mirror. As this book will show, sometimes these problems were far more severe in the past, as in the Cold War or in previous historical epochs like the interwar period in Europe. Friction is inevitable in alliance politics, especially when adversaries pose new threats and challenges. Just as in the past decision-makers were able to confront those challenges with some success, so they look poised to do so again. Contrary to appearances, the end of most US alliance commitments is not upon us. For all the vitriolic rhetoric about free-riding allies, the United States in fact stepped up its military commitments to Europe during Trump’s presidency, with an increased presence in both Germany and Poland. Trump did not withdraw major numbers of military forces from any treaty ally, despite a late effort to rearrange US force posture in Europe (Lanoszka and Simón 2021). Under his administration, the United States acquired new treaty allies when Montenegro and North Macedonia joined NATO in 2017 and 2020, respectively.
That said, as the events in 2008 demonstrated, changes are afoot in world politics that portend important adjustments in US security guarantees in Europe and East Asia, on the one hand, and, on the other, military partnerships that involve China, Russia, or both. These changes are not reducible to the personal character or rhetoric of any one leader, including someone like Trump, Putin, or even Xi. Rather, these changes reflect a transforming international environment characterized by the rise of China, the roguishness of Russia, and the maturation and proliferation of once cutting-edge technologies like precision strike as well as the malicious use of cyber operations and disinformation campaigns. In fact, these changes had already begun years before Trump declared his candidacy for the US presidency, and will continue to unfold into the future. After all, alliance politics is usually marked by divergent geopolitical interests, worries about the consequences of commitment-making, and, in today’s technological context, burden-sharing controversies. These issues will shape alliance politics going forward even if Trump’s successor, Joseph Biden, has consistently spoken favorably of US military alliances. The SARS-CoV-2 pandemic could accelerate these trends as countries grapple with its economic and political fallout.
The Arguments of this Book
Alliance politics will remain a persistent feature of international affairs, but, as this book argues, that is because military alliances operate in ways that are often surprising, counterintuitive, and difficult to understand. To see why, consider the following standard claims that scholars and practitioners often make regarding how alliances function, or should function, from when these arrangements are first negotiated to when they meet their eventual demise. In outlining, in the discussion below, what those pieces of conventional wisdom are and why they are problematic, I offer a preview of the argument that each chapter in this book advances.
Conventional wisdom #1: States form alliances to balance power and/or to gain influence over other states
Many observers agree that states form military alliances in order to aggregate power in the face of a security challenge or to gain influence over another. Sometimes both motives are operative. There is much to be said for this canonical understanding of alliance formation: it is intuitive and easy to grasp.
Still, as shown in Chapter 1, although balancing power and influence-seeking can drive particular instances of alliance formation, these explanations are at best insufficient and may not even identify conditions necessary for states to agree to a military alliance. They indeed tend to overpredict how many alliances actually form. Most importantly, it is unclear why having a written alliance by way of a treaty is at all necessary for balancing power against adversaries or for projecting influence over would-be allies.
Writing down an alliance commitment accomplishes two strategic but seemingly contradictory tasks. One is that it allows signatories to communicate to international and domestic audiences that they have a serious stake in addressing a particular security challenge. Another is that it permits the signatories to leave purposely vague the conditions under which a treaty obligation would become operational, keeping both allies and adversaries in the dark as to what exactly would trigger a major defensive response. This vagueness is important in part because treaty allies have similar but not identical interests. Differences, just as much as commonalities, drive the need for written commitments. Treaties enable states to thread the needle more effectively between certifying a commitment for augmenting deterrence and allowing for enough ambiguity to keep allies and adversaries alike off balance. This in turn can lead the way for even more military cooperation because states become more comfortable about investing in their security relationship. Nevertheless, some alignments between states never rise to the level of a written commitment because their differences outweigh those commonalities too much.
Conventional wisdom #2: The alliance dilemma is a fundamental problem shared by all military alliances
Scholars and observers frequently allude to something called the alliance dilemma to highlight the steep trade-offs that come with commitment-making in the face of possible war. When providing an ally with a broad military commitment, a state may worry that the benefiting ally would be emboldened to have a more aggressive foreign policy than it would otherwise have, thereby upping the risk of some undesirable war. However, weakening a military commitment to offset those so-called entrapment risks could leave the receiving state fearful that its allies will abandon it to the depredations of an adversary. Entrapment and abandonment are thus two sides of the same coin, with severe trade-offs confronting decision-makers when they are designing and managing alliances.
How severe is the alliance dilemma? Chapters 2 and 3 explore the issues of entrapment and abandonment, respectively, to build up an argument that this dilemma is not really a dilemma. The problems highlighted here are instead tractable; certainly, they are not endemic to all alliances. Chapter 2 notes the different sources of entrapment risks that exist and what strategies allies can adopt to mitigate them. These sources can be the alliance treaty itself, systemic factors like polarity and the offense–defense balance, obsession with reputation, and transnational ideological networks. Sometimes these risk factors can be mutually reinforcing; sometimes they can cancel each other out. Nevertheless, although entrapment is empirically rare, the historical record reveals that decision-makers do genuinely worry about it. But precisely because they take it seriously, entrapment becomes a self-denying prophecy. As for abandonment fears, no state should ever be rationally confident that it would receive support from a defender against a militarily capable adversary. Chapter 3 explains that, although abandonment fears are
