Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Political Science

First Advisor

Brendan O'Leary


Since 2015 over two million people have been expelled, en masse, around the world. Mass expulsion is a major international issue that threatens peace and security around the globe. This dissertation examines why and how governments expel ethnic groups en masse. What motivates them to implement an expulsion policy and why don’t more governments do the same? By isolating policies of intentional group-based population removal—distinct from genocide, massacre, and coercive assimilation—I show that the motivations of expulsionist governments are informed by the phase of nation-building and the perceived threat of the target group. The four clusters of motivations are: fifth column, anti-colonialism, nativism, and counterinsurgency/reprisal. Since not all governments with one of the identified motivations to expel go on to remove populations en masse, I also identify important constraints on governments’ strategic choices. Through four paired-comparison case studies of similarly motivated governments with different outcomes (expulsion or non-expulsion), I show that alliances, target group homeland state(s), and the international community are the key contributing factors that enable or deter mass expulsion policies. The evidence is drawn from archival research conducted at the United Nations High Commissioner for Refugees, the International Committee of the Red Cross, and the League of Nations archives in Geneva, Switzerland, as well as from other primary sources, secondary historical sources, and extant datasets. This dissertation contributes to the field of ethnic conflict and exclusionary politics. It fills a gap in the literature by systematically examining mass expulsion policies that intentionally remove ethnic groups over the longue durée. The argument expands existing explanations beyond war and security threats to highlight an entire class of expulsions that target economic threats, which requires scholarly and international policy attention. The dissertation also deepens our understanding of critical atrocity constraints and proposes tangible policy recommendations for deterring its use.

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