This book examines the development of the modern idea of militarism from its inception in the 1860s until the outbreak of World War I. Often regarded as the archetypical militarist state, imperial Germany in fact witnessed a major controversy over the issue, which became a touchstone of political opposition. Issues like the arms race and the military-industrial complex displaced more traditional concerns about authoritarian rule, and militarism gradually acquired its modern meaning. The book is part of a wider discovery by historians of the way political identities and ideas intermeshed, contributing to the rise of civil society and new types of politics in modern Europe. The political history of the main protagonist of anti-militarism, German social democracy, is cast in a new light, as Nicholas Stargardt reveals the lasting influence of older radical traditions and reappraises the role played by its espousal of Marxism.