Violence and Ethnic Segregation: A Computational Model Applied to Baghdad


  • Authors' notes. Previous versions were presented at the 2010 Annual Meeting of the American Political Science Association, Washington DC, the 2009 Meeting of the Peace Science Society, and the New Faces in Political Methodology III conference, Penn State University, May 2010. We are grateful to the Empirical Studies of Conflict project at Princeton University (especially Jacob N. Shapiro and Joseph H. Felter) for access to the SIGACTS data, and to the International Conflict Research group at ETH Zurich for providing the computational infrastructure. Nils Weidmann gratefully acknowledges support from the Air Force Office of Scientific Research (grant #FA9550-09-1-0314), and from the Alexander von Humboldt Foundation (Sofja Kovalevskaja Award). This and prior versions of this paper benefited significantly from comments by Navin Bapat, Andrew Enterline, Cullen Hendrix, Jacob Shapiro and Richard Stoll, as well as three anonymous reviewers at ISQ. An online appendix is available at


The implementation of the United States military surge in Iraq coincided with a significant reduction in ethnic violence. Two explanations have been proposed for this result: The first is that the troop surge worked by increasing counterinsurgent capacity, whereas the second argument is that ethnic unmixing and the establishment of relatively homogenous enclaves were responsible for declining violence in Baghdad through reducing contact. We address this question using an agent-based model that is built on GIS-coded data on violence and ethnic composition in Baghdad. While we cannot fully resolve the debate about the effectiveness of the surge, our model shows that patterns of violence and segregation in Baghdad are consistent with a simple mechanism of ethnically motivated attacks and subsequent migration. Our modeling exercise also informs current debates about the effectiveness of counterinsurgency operations. We implement a simple policing mechanism in our model and show that even small levels of policing can dramatically mitigate subsequent levels of violence. However, our results also show that the timing of these efforts is crucial; early responses to ethnic violence are highly effective, but quickly lose impact as their implementation is delayed.