Given the dangers of war, states should carefully tailor their alliances to specific threats and constraints. We expect wide variety in security strategies and pact designs. This expectation is wrong. In any year, 75 percent of states pursue identical alliance strategies. Why do countries ignore their individuated conditions and converge on a single dominant alliance strategy? This chapter presents the book's puzzle, describing patterns in alliance design from 1715–2003.

This chapter offers a social theory of diffusion to explain the dominant alliance strategy. Major wars shatter the international system. Into this breach, a new hegemon creates a core pact targeting its central security challenge. This partnership becomes the standard for credible and legitimate security policy in the postwar environment. Secondary countries copy its strategy to demonstrate the credibility of their own alliances. Peripheral nations emulate to acquire international status and prestige.

This chapter uses quantitative analysis to determine that the core alliance systematically produces the dominant strategy. Seven statistical tests probe the theory's causal foundations and mechanisms, providing reinforcing support for the book's argument. The dominant strategy is statistically linked to social proof and validation, credibility concerns, international norms, and legitimacy.

The book's first case study demonstrates how the dominant strategy constrains even the great powers' alliance choices. It explores the core European pacts between Germany, Austria-Hungary, and Russia from 1873–1890. These countries repeatedly established alliances to solidify their security relations, and they repeatedly failed. Austria-Hungary prevented Germany from displacing it from the heart of Berlin's alliance strategy. Consequently, these three conservative empires were unable to manage deep, intra-allied disputes. Network constraints prevented the fluid, transactional balancing strategies, contributing to World War I's onset.

The second case highlights how Middle East and Southeast Asian countries pushed the United States to create NATO-like security institutions in their regions early in the Cold War. These countries evaluated American reliability based on alliance emulation: only strategies matching NATO's design signaled commitment. Washington's refusal to adopt the Atlantic Alliance's strategy in other alliances undermined efforts to demonstrate resolve and consolidate power against the Soviet Union.

The final case details the role of alliance construction in southern Africa's status-building policy following the Cold War. Suddenly bereft of superpower patronage, these countries viewed NATO and Europe more broadly as the most effective strategy to foster military security and economic development in their region. But southern Africa was politically unsuited to such a strategy, leading states to seize alliance leadership to advance their own unilateral policies. These countries nevertheless continued to model NATO to legitimate their security strategy and foreign policy goals.

Copying the dominant strategy reduces the risk of alliance failure by one-third. This chapter leverages statistical methods to link emulation to security behavior. Military partnerships are more reliable and cohesive when they converge on a single, socially accepted standard of credible and legitimate cooperation. Scholars often assume that institutionalization enhances reliability. This chapter demonstrates that such assumption is only true when the core alliance is itself institutionalized. If not, formal coordination can increase the risk of alliance failure by 26.46 percent.

This concluding chapter calls for a "NATO in Asia" as the only credible demonstration of American commitment to the region against an assertive China. It draws out policy implications from the theory for international order, the feasibility and drawbacks of transactional foreign policies, and major war.