This impressive study provides one of the best efforts yet to understand how and why states have built coalitions to pursue military operations in the face of human atrocities, terrorism, and the threat of weapons of mass destruction. Surveying dozens of military operations since the end of World War II, Henke shows that coalitions rarely emerge naturally in response to shared perceptions of threats, through a convergence of momentary interests, or from the coercive efforts of a hegemonic power. They need to be built by “pivotal states” that can overcome obstacles to collective action and orchestrate complex military operations. Henke looks closely at the coalition-building processes around the Korean War in the 1950s, the Australian-led operation in East Timor in 1999, the UN deployment in Darfur in 2007, and the EU interventions in Chad and the Central African Republic in 2008. Henke finds that building coalitions requires “embedded diplomacy”—a pivotal state’s complex array of institutional connections and networks of relations with other states—which creates ways for officials to make commitments, bargain, exchange information, and broaden the scope of negotiations to include other issues. Henke demonstrates the importance of diplomacy and leadership in building a successful coalition but does not try to determine in which circumstances the use of military force was (or would be) wise or just.