Unruly Friends: Grand Strategy and Strategic Incoherence in Military Alliances

When a great power attempts to check a rival, why do its allies sometimes reconcile their military capabilities with its grand strategy and sometimes appear reluctant or unable to do so? Over the decades, numerous scholars, policymakers, and pundits have come to believe that they understand the sources of strategic incoherence in military alliances. The conventional wisdom—i.e., the “collective goods theory” of alliance security—holds that states have chronic temptations to free-ride on the preponderant ally’s military efforts. To the extent the leading power overcommits resources towards confronting the adversary, its allies will have few incentives to revise their military postures in line with its strategic aims. If this logic is correct, the chief explanation for why a great power like the United States often finds it difficult to achieve strategic coherence in its alliance relationships lies in its own excesses. Once it dials back its security commitments, so the argument goes, allies will finally pull their own weight. I argue that this conventional wisdom is wrong. Strategic coherence in military alliances is not uniformly conditioned by the generosity of the leading power’s security commitments. Instead, my “demand-side theory” of strategic coherence highlights the interaction between the leading power’s grand strategy and the military vulnerability of its allies. Leading powers need allies to bring specific kinds and amounts of military capabilities to the table in order to effectively implement their preferred grand strategies. However, adopting the “appropriate” capabilities is often prohibitively difficult for allies because it requires them to take on awful risks to their fundamental security interests. Doing so may, in particular, trigger unbearably costly countermeasures from the adversary or create otherwise avoidable deficiencies in their military competitiveness. Developing these insights, I argue that strategic incoherence is especially likely when (1) the leading power tries to “outsource” military capabilities to an ally that is highly vulnerable to military predation, or alternatively when (2) its grand strategy is predicated on “insourcing” military capabilities while limiting those of a relatively invulnerable ally. Using detailed case studies of the United States’ Cold War alliances with France and West Germany, the Soviet Union’s alliances with China and Cuba, Great Britain’s alliances in the early 20th century, and the United States and China’s East Asian alliances in the post-Cold War period, I identify the remarkably demanding conditions under which alliances in the modern era have achieved strategic coherence. This effort draws heavily on archival material and, for the contemporary East Asian cases, semi-structured interviews with regional policymakers