Numerous studies have found that, in general, democracy decreases intensity of ethnic rebellion. However, the recent transition experiences of multinational states problematize the assumption that social peace accompanies democratization. Especially in the post-Communist world, democratization has been followed by increases in ethnic rebellion. This dissertation explores the question of why some ethnic groups maintain or increase levels of rebellion following democratization while others rely on nonviolence or at least decrease the level of violence employed against the state. I conduct a large-N cross-national comparative investigation of these questions, employing Barry Weingast's (1998) reciprocal vulnerability framework, focusing on the impact of conflictual histories, political institutions, form of democratization and uncertainty. The analysis includes 102 ethnic groups in 42 countries that attempted democratization between 1980 and 2000 and employs data from the Minorities at Risk dataset, the Polity dataset and original data on ethnic participation in democratization, autonomy and federalism, and repression. Multiple statistical methods are employed to test 13 hypotheses derived from the reciprocal vulnerability framework. Findings provide only limited support for reciprocal vulnerability as a generalizable explanation of ethnic rebellion. However, findings strongly support grievance-based theories of ethnic rebellion, and provide limited support for collective action theory of ethnic rebellion, particularly in terms of the effects of repression.