Why do some military and rebel groups commit many types of violence, creating an impression of senseless chaos, whereas others carefully control violence against civilians? A classic catch-22 faces the leaders of armed groups and provides the title for Amelia Hoover Green's book. Leaders need large groups of people willing to kill and maim-but to do so only under strict control. How can commanders control violence when fighters who are not under direct supervision experience extraordinary stress, fear, and anger? The Commander's Dilemma argues that discipline is not enough in wartime. Restraint occurs when fighters know why they are fighting and believe in the cause-that is, when commanders invest in political education. Drawing on extraordinary evidence about state and nonstate groups in El Salvador, and extending her argument to the Mano River wars in Liberia and Sierra Leone, Amelia Hoover Green shows that investments in political education can improve human rights outcomes even where rational incentives for restraint are weak-and that groups whose fighters lack a sense of purpose may engage in massive violence even where incentives for restraint are strong. Hoover Green concludes that high levels of violence against civilians should be considered a "default setting," not an aberration.