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 normal in the face of an external threat, such fears seldom reach a level of intensity that leads states to consider neutralism or nuclear proliferation. This chapter probes the factors that can affect the intensity of abandonment concerns and discusses how states practice reassurance to convince allies that their security concerns are being addressed.
Taken together, the punchline of Chapters 2 and 3 is that the alliance dilemma is not as pronounced as often asserted because tools are available for addressing it. The trade-offs implied by the dilemma do not always exist. Sometimes states are so aligned in their political interests with one another vis-à-vis their adversaries that they simply do not face such conundrums in their alliance decision-making. Still, certain measures that some observers advocate for addressing contemporary forms of subversion may not be necessary and may even be counterproductive with respect to reassuring worried allies.
Conventional wisdom #3: Members of US alliances must do more to bear their fair share of the common defense burden
President Trump frequently chided allies in Europe and East Asia for not spending enough on their militaries and thus not bearing their share of the collective defense burden. He menacingly threatened abandonment in pushing NATO members to spend 2 percent of their gross domestic product (GDP) on defense so as to fulfill the pledges made in 2014. Yet, among US presidents, Trump was unique mostly only in tone. Many of his predecessors had complained that US allies could do more to bear the burden more equitably. During the Cold War, US presidents were exasperated by the perceived inadequacy of their allies. Though these alliance criticisms have been around for a long time, such complaints have gathered force in more recent times because the United States is not as powerful as it used to be.
The premise of most contemporary burden-sharing controversies, financially grounded as they often are, is a faulty one, however. The presumption is that allies could contribute to the common defense burden in a more equitable manner. That sounds reasonable enough, but what does it really mean in practice? Chapter 4 notes that part of the reason why burden-sharing controversies arose in the first place is because of how military alliances have come to last longer, a result of how war itself has become so costly in light of nuclear weapons. Crucially, advances in military technology create contradictory incentives when it comes to defense spending. On the one hand, the growing sophistication and complexity of weapons platforms require sustained long-term investment on the part of states to ensure that their militaries do not lag behind their competitors or even allies. On the other hand, nuclear deterrence may make militarized conflict less likely, which in turn drives down the willingness of states to spend on defense. Some states might even believe that spending on conventional military power could make nuclear war more probable. The relationship between defense spending and the collective good of deterrence is, to say the least, hardly linear. Common thresholds for evaluating defense contributions – as in the 2 percent guideline used by NATO – make little sense.
Conventional wisdom #4: Military alliances aggregate capabilities and thus allow their members to confront security challenges more effectively
Recall the earlier standard claim that one motivation for forming alliances is to balance against a shared threat. One implication of this claim is that states can see off their security challenges more effectively in unison with their allies, provided that they have some, than they would without them.
This view is plausible, but Chapter 5 argues that it is at best incomplete. Most, if not all, present-day alliances exist to prevent war, but no US-led (or even Soviet/Russian) alliance since the end of the Second World War has fought directly against its primary adversary. In fact, alliances generally do not fight wars – ad hoc arrangements like coalitions do. And when wars are fought or multinational military campaigns are undertaken, treaty allies often work alongside nontreaty partners in those coalitions to advance common, but usually not identical, goals. Their motivations for participating in those operations may vary, especially when their own alliance obligations may not be directly relevant to the campaign at hand. Moreover, capability aggregation hardly guarantees military effectiveness. One might think that alliances serve to aggregate capabilities, implying that the more military power and the more members there are, the more effective and successful these alliances would be against adversaries. However, strategic, organizational, and technical factors can create a range of problems that hamper the ability of coalitions in going about multilateral military operations as successfully as they would like. That said, military alliances may still be more effective fighting organizations thanks to the joint military exercising and standardization that can occur under their auspices, but that would not be because they simply aggregate capabilities.
Conventional wisdom #5: Military alliances are only useful for as long as the strategic circumstances that led to their emergence hold
Proponents of one school of thought – realism – contend that a military alliance exists, or at least should exist, in proportion to the strategic need that gave rise to it. To consider again the first standard claim described earlier, if states no longer have to balance against a particular threat or to have influence over another state for whatever reason, then the military alliance founded for advancing such interests should cease to exist.
Military alliances can end for different reasons, though. In discussing how alliance treaties have historically defined the terms of their expiry, Chapter 6 outlines how alliances have historically come to an end: fulfillment of their original functions, military defeat, downgrading, unilateral abrogation, and transformation. A key observation made in Chapter 6 is that the factors that push states to establish alliances are seldom the factors that explain why those alliances meet their demise. Sometimes the strategic need that spurs the creation of the alliance outlasts that alliance. The view that alliances should only exist as a function of specific needs and