I am Professor and Chair of the Political Science Department at The University of Pennsylvania. I write on civil wars and ethnic conflict in the fields of international relations and comparative politics. Published work in these areas has appeared in the American Political Science Review, International Organization, World Politics, The Journal of Conflict Resolution, Perspectives on Politics, and other journals. I co-authored Making War and Building Peace (Princeton University Press, 2006), the first book to analyze the impact of UN peace operations in post-conflict transitions; and Breaking the Conflict Trap: Civil War and Development Policy, one of the first quantitative studies of the causes of civil war around the world. In a two-volume book project (Understanding Civil War: Evidence and Analysis) I developed a nested research design for the quantitative and qualitative study of civil wars. I currently direct Penn’s Identity & Conflict Lab, an inter-disciplinary group working on a broad range of topics, including the effects of external intervention on ethnic polarization; the stability of postwar ethnic power-sharing; the causes of escalation of non-violent conflicts over self-determination; the effect of norms on inter-group conflict and discrimination against immigrants; the effect of economic hardship on pro-social behavior; the long-term legacies of violence exposure among refugee populations; the sources of national identification; and the effects of integrative institutions on the salience of ethno-regional identities. An ongoing (though slow-moving) project is a new book on IR theory that integrates political science theories of international conflict and cooperation with social-psychological theories and evidence on identity formation and inter-group conflict.