Scholars often debate the future of the modern system of nation-states, but rarely do they study its origins. This groundbreaking book provides a sweeping reinterpretation of the religious and geopolitical conflicts of the seventeenth century, culminating in the emergence of the European state system. Nexon focuses on the pivotal role of the Protestant Reformation in precipitating crisis across premodern Europe. What threatened weak leaders was less the religious ideas themselves than the rapid proliferation of social movements and transnational forms of collective action. New religious identities undermined old arrangements of rule, triggering general upheaval, revolts, and the Thirty Years' War, which, in turn, yielded a new European order. Nexon takes issue with traditional accounts that fixate on power politics and the rise and decline of empire or emphasize changing conceptions of sovereignty. In his telling, it is the rapid emergence of transnational religious movements that altered the viability of states and fostered geopolitical competition. Historically minded scholars will enjoy Nexon's detailed studies of the Hapsburg empire and the French wars of religion. Students of contemporary world politics will find relevance in his account of how transnational networks -- religious or otherwise -- can undermine the authority of states and trigger new forms of collective action.