This book examines a variety of comparative and historical experiences in which irregular armed forces (ranging from militias, paramilitaries, guerrillas, bandits, mercenaries, vigilantes, and police forces to armed veteran groups) have struggled against or on behalf of national states. The study hopes to raise questions about the new political relevance of these types of armed forces. It considers the conditions under which they are more significant than conventional military personnel in supplanting or undermining states, and their broader role in national political development.