Colonial warfare has been a frequent and bloody feature of international relations, yet most studies of wartime civilian victimization focus on either interstate or civil wars. In this article I argue that ignoring colonial violence has distorted our understanding of state-directed violence against civilians in wartime. I introduce a new theory of colonial violence, which focuses on the distinctive strategic, normative, and institutional incentives that colonial powers have to harm civilians. To assess this theory, I introduce and analyze a new data set of 193 cases of colonial war from 1816 to 2003. Using a variety of measures of civilian harm, I find that colonial wars are especially brutal. Three-quarters of states in colonial wars targeted civilians, for example, compared to less than a third of states in interstate wars. But some colonial wars are harder on civilians than others. Colonial powers are more likely to harm civilians when their indigenous adversaries employ guerrilla tactics, when their indigenous adversaries come from a different perceived racial background, and when the colonial state relies on settlers or indigenous intermediaries to help compensate for its relative weakness. By ignoring colonial violence in world politics, we misunderstand the scale and scope of state-directed violence against civilians and miss an opportunity to deepen our understanding of the causes of this brutality.