What do we know about war? This much-anticipated reference book analyzes more than a thousand wars waged from 1816 to 2008 using authoritative, highly standardized, and systematic coding methods from the Correlates of War Project, which aims to reveal the underlying patterns and causes of war. Resort to War lists and categorizes all violent conflicts with 1,000 or more battle deaths and provides an insightful narrative for each struggle. The volume distinguishes between traditional interstate war, the phenomenon of extra-state war as evidenced by the Al Qaeda–USA conflagration, intra-state war, and the new category of nonstate ethnic wars. After explaining how to determine what a “state” is and how to classify different types of wars, the authors describe each encounter and highlight major patterns across eras and regions, identifying which categories of war are becoming more or less prevalent over time, and revealing connections between the different types of war. Resort to War, the second title in the Correlates of War Series, is a definitive source for students and researchers examining patterns of international conflict; it is the essential guide to the data, trends, and context of these violent encounters.