This dissertation analyzes the causes of ethnic cleansing defined as forced population movements and killings that specifically target ethnic groups. To explain ethnic cleansing, I start from the question of "what is ethnicity?" While not denying that ethnic groups are politically constructed, I argue that there is also a generally applicable geographical or spatial basis to ethnic groups. Because of this geographical basis, when territory-seeking actors wage war they form alliances with ethnic rather than other types of groups in the contested territory. These alliances result in mass deportations or killings at the beginning of wars or in the aftermath of failed occupations.

To test this argument, I use an original dataset of minority-state dyads in Europe 1900-1950 and trace the evolution of state-ethnic minority relations in several historical contexts. I also use sub-national level research in the context of Bosnia to evaluate the predictions of the theory for the behavior of non-state actors. I conclude by exploring the implications of my argument for the macro-regional distribution of ethnic cleansing.

The project makes important contributions to the study of mass ethnic violence in particular and political violence in general. First, I adopt a new approach to ethnicity which highlights its geographical foundations and distinguishes it from other political cleavages. This conceptualization offers a fresh understanding of the conditions that make ethnicity more salient than other cleavages and the conditions that exacerbate the relations between ethnic groups. Second, my dissertation provides a unified theoretical framework that can predict the targets and timing of ethnic cleansing. Hence it improves on the existing arguments which often rely on disparate causal logics to account for the target and the timing of ethnic cleansing. Finally, the project significantly improves on the existing literature in terms of empirical breadth and rigor.