This book explains the creation of the European Union's Security and Defence Policy - to this day the most ambitious project of peacetime military integration. Whether hailed as a vital step in the integration of Europe or berated as a wasteful threat to U.S. power, European citizens are increasingly interested in the common defence policy. Today, "European Defence" is more popular than the European Union itself, even in Great Britain. Mérand addresses the fundamental challenge posed by military integration to the way we think about the state in the 21st Century. Looking back over the past 50 years, he shows how statesmen, diplomats and soldiers have converged towards Brussels as a "natural" solution to their concerns but also as something worth fighting over. The actors most closely associated to the formation of nation-states are now shaping a transgovernmental security and defence arena. As a result, defence policy is being denationalized. Exploring the complex relations between the state, the military, and citizenship in today's Europe, Mérand argues that European Defence is a symptom, but not a cause, of the transformation of the state. This book is an original contribution to the theory of European integration. Drawing on the work of Pierre Bourdieu, Mérand develops a political sociology of international relations which seeks to bridge institutionalism and constructivism. His careful study of practices, social representations and power structures sheds new light on security and defence cooperation, but also on European cooperation more generally.