To understand the spread of nonstate violence, Thomas focuses on the crucial role played by an epochal transformation in international norms. Since the eighteenth century, the Westphalian model of sovereignty has reserved the legitimate use of force to states. Thomas argues that normative changes in the decades after World War II produced a "crisis of coherence" for formal and informal rules against nonstate violence. In detailed case studies of nonstate militias, transnational terrorist networks, and private military contractors, Thomas explains how forces contesting state prerogatives exploited this crisis, which in turn reshaped international understandings of who could legitimately use force. By considering for the first time all three purveyors of nonstate violence as aspects of the same phenomenon, The New Dogs of War explains this fundamental shift in the norm that for centuries gave states the monopoly on military force.