In this deeply informed book, renowned historian Jeremy Black addresses the crucial question of why wars happen, bridging the disciplines of history, political science and international relations, and spanning over the centuries. Black marshals an astonishing range of material from all corners of the globe, and demonstrates the universalities of conflict. What then causes wars? Do they primarily reflect bellicosity in societies and states, or do they arise as the result of the breakdown of diplomatic systems? How far are the causes of war related to changes in the nature of warfare, of the international system or of the internal character of states? Black looks at the problems of deepening war, and analyses the three main forms of conflict: wars across cultures, wars within cultures and civil war. He also assesses the present situation and asks where we are heading in terms of future wars.