What Do We Know about War? reviews the research on causes of war and the conditions of peace in the past forty-five years. Leading scholars explore the critical roles of territorial disputes, alliances, arms races, rivalry, and nuclear weapons in bringing about war as well as the factors promoting peace, including democracy, norms, stable borders, and capitalist economies. Considering what has been learned about the causes of war and the conditions of peace in the ten years since the publication of the first edition, this invaluable text offers an accessible and up-to-date overview of current knowledge and an agenda for future research.