This interdisciplinary book is the first systematic study of the relationship between nationalism and war and, as such, makes an original contribution to theories of nationalism and state formation. It offers a dynamic and interactive framework by which to understand the role of warfare in its changing manifestations in the rise of nation-states, the formation of national communities, definitions of political rights and duties, and the transformation from a world of empires to one of nation states. Nationalism and War scrutinizes existing approaches that view both nations and nationalism as recent products of martial state-building that began with the military revolutions in Europe, and argues that nationalism and national communities emerged independently in the Middle Ages to shape both war-making and state-building. This book also explores the connection between war commemoration and the creation of nations as sacralized communities that offer meaning and purpose to a world marked by unpredictable change. It shows how nationalist military revolutions led to the downfall of Empires in total war and the mass production of postcolonial nation states. But problems of security have also inspired recurring patterns of re-imperialization. This book refutes claims that we are now in a global and post-national era where traumatic accounts have replaced the heroic narratives that once sustained nation-states. Finally, it appraises approaches that claim there is an inherent connection between nationalism and collective violence, arguing such connections are largely contingent.