Why do states and peoples go to war? Conversely, how can war be avoided? This course surveys some of the most important explanations--including human nature, the anarchic international system, domestic politics, economics, technology, nationalism and terrorism--and evaluates them in light of historical wars, and of crises resolved short of war. Cases include the Peloponnesian War, the Napoleonic Wars, World War I, World War II, the Cuban missile crisis, ex-Yugoslavia's wars, and September 11.