Theorists of ethnic conflict have argued that the physical separation of warring ethnic groups may be the only possible solution to civil war. They argue that without territorial partition and, if necessary, forced population movements the war cannot end and genocide is likely. Other scholars have counterargued that partition only replaces internal war with international war, that it creates undemocratic successor states, and that it generates tremendous human suffering. This debate has so far been informed by very few important case studies. This article uses a new data set on civil wars to identify the main determinants of war-related partitions and estimate their impact on democratization, on the probability that war will recur, and on low-level ethnic violence. This is the first large-N quantitative analysis of this topic, testing the propositions of partition theory and weighing heavily on the side of its critics. Most assertions of partition theorists fail to pass rigorous empirical tests. The article also identifies some determinants of democratization after civil war, as well as the determinants of recurring ethnic violence. These empirical findings are used to formulate an alternative proposal for ending ethnic violence.