Why do actors switch sides in civil wars? And why do many of these conºicts feature systematic re- alignments among competing actors? Numerous conºicts include instances of defection with far-reaching implications. In Afghanistan, efforts to build a co- hesive army have been hampered by instances of Hazara, Tajik, and Uzbek com- manders defecting from the Afghan government and NATO coalition forces to join their erstwhile Taliban enemies. 1 The crisis unfolding in the Central African Republic, escalated by the coup against François Bozizé in March 2013, was pre- cipitated by the defection of many of the same “liberators” who brought his government to power in 2003. 2 Violence in Somalia has been driven by a repeti- tive cycle of fragmenting alliances among factions. Al-Shabaab’s relative military success in Somalia from 2007 to 2010 owed much to its ability to forge a degree of cohesion and prevent defections. 3 In the eastern Democratic Republic of Congo, repeated failures to integrate armed groups into national institutions have led to a cycle of mutinies, sparking humanitarian crises. 4 In these and other wars, some factions switch sides as if passing through a re- volving door. Unstable alignments among fragmenting factions are more than just a characteristic of these wars—in many ways, they are the war, with re- peated side switching fueling cycles of protracted violence. Alignments in civil wars explain important outcomes, as illustrated by Lee J.M. Seymour is Assistant Professor of Political Science at the University of Amsterdam. The research for this article was funded by a Veni research grant from the Dutch Scientiªc Organi- zation. The author is grateful for research assistance from Anna Morath and comments from Ariel Ahram, Kristin Bakke, Kathleen Gallagher Cunningham, Ursula Daxecker, Lotje de Vries, Maria Koinova, Jorg Kustermans, Bethany Lacina, Romain Malejacq, Theodore McLauchlin, Sabine Otto, Costantino Pischedda, Andrea Ruggeri, Marieke Schomerus, Henning Tamm, Rebecca Tromble, and the anonymous reviewers. 1. Antonio Giustozzi, “The Taliban beyond the Pashtuns,” Afghanistan Papers No. 5 (Waterloo, Canada: Centre for International Governance Innovation, July 2010). 2. International Crisis Group, “Central African Republic: Priorities of the Transition,” Africa Re- port No. 203 (Brussels: International Crisis Group, June 11, 2013). 3. Stig Jarle Hansen, Al Shabaab: The History and Ideology of a Militant Islamist Group 2005–2012 (Oxford: Oxford University Press, 2013). 4. International Crisis Group, “Eastern Congo: Why Stabilization Failed,” Africa Brieªng No. 91 (Brussels: International Crisis Group, October 4, 2012); and Timothy Raeymaekers, “Post-War Conºict and the Market for Protection: The Challenges to Congo’s Hybrid Peace,” International Peacekeeping, Vol. 20, No. 5 (November 2013), pp. 600–617. Why Factions Switch Sides in Civil Wars Why Factions Switch Sides in Civil Wars Lee J.M. Seymour Rivalry, Patronage, and Realignment in Sudan International Security, Vol. 39, No. 2 (Fall 2014), pp. 92–131, doi:10.1162/ISEC_a_00179 © 2014 by the President and Fellows of Harvard College and the Massachusetts Institute of Technology. 92