Civil War Intervention and the Problem of Iraq 1 Stephen Biddle Council on Foreign Relations Jeffrey A. Friedman Harvard Kennedy School AND Stephen Long University of Richmond Outside intervention in civil warfare is important for humanitarian, theoretical, and practical policy reasons—since 2006, much of the debate over the war in Iraq has turned on the danger of external intervention if the United States were to withdraw. Yet, the literature on intervention has been compartmented in ways that have made it theoretically incomplete and unsuitable as a guide to policy. We therefore integrate and expand upon the theoretical and empirical work on intervention and apply the results to the policy debate over the US presence in Iraq using a Monte Carlo simulation to build upon the dyadic results of probit analysis. We find that Iraq is, in fact, a significantly intervention-prone conflict in an empirical context; the prospect of a wider, regional war in the event that violence returns in the aftermath of US withdrawal cannot safely be ignored. Civil war is the most common form of armed conflict worldwide and has killed tens of millions of people in the decades since World War II. It poses many impor- tant theoretical and empirical questions, but one of the most important is that of foreign intervention. Warfare internal to a state is bad enough, but if inter- vention causes the war to spread across borders, a local internal tragedy can become a region-wide con- flagration with far worse consequences for much greater populations. 2 Its stakes make the causes and incidence of civil war intervention an inherently important question for scholarship. Intervention is also an important issue for US for- eign policy in the form of the post-2003 civil war in Iraq and its potential consequences. By invading Iraq and triggering a civil war, US policy created a risk that this internal conflict would spill over its borders and draw Iraq’s neighbors into a wider war with potentially severe humanitarian and international economic effects. Iraq is a nation of 30 million in the heart of the Middle East’s oil fields. Warfare lim- ited to Iraq is bad, but if intervention by Iraq’s neighbors creates a regional conflict, the result could be a major increase in the suffering of inno- cents and a serious blow to global energy markets in a time of extraordinary economic fragility. In fact, preventing the war from spreading via for- eign intervention has become the chief US strategic interest in the conflict since the civil war escalated in intensity in 2004. Ever since that time, much of the US debate on the war has effectively turned on the relative merits of persisting in the conflict in the hope of resolving it successfully, as opposed to removing US forces would risk an escalation of civil conflict that could cause a regional war. Opponents of withdrawal have typically argued that removing US forces would risk a regional war as neighbors inter- vene to protect their interests, and that this risk mili- tates against withdrawal (for example, Byman and Pollack 2007; National Intelligence Council 2007; Boot 2008a). Proponents of withdrawal have often argued, inter alia, that this risk is exaggerated and that US forces could leave Iraq safely without trigger- ing a wider war (for example, Simon 2007, 2008; Gause 2008; Korb, Katulis, Duggan, and Juul 2008). Today, Iraq’s civil war is in remission and the Uni- ted States is committed to withdrawal. The pace of this drawdown remains controversial, however, and the same issues now underlie this new debate. Oppo- nents of full withdrawal argue that it risks reigniting 1 For helpful comments on earlier drafts, the authors would like to thank James Fearon, Christopher Moore, Dan Reiter, Joshua Rovner, Alan Stam, and the members of the George Washington University Institute for Global and International Studies. 2 Note that intervention per se is not necessarily destabilizing; if used as a form of multilateral conflict management by benign outside powers, it can be a means of ending or moderating a war rather than expanding it. Several studies examine the role of external intervention on the duration of civil wars, including Balch-Lindsay and Enterline (2000), Regan (2002), Regan and Aydin (2006), and Cunningham (2010). Our interest, however, is with third-party motives and methods that do not conduce to stability. As we note below, our definition of ‘‘intervention’’ is restricted to the most forceful of the forms addressed in the broader intervention literature to date, and we exclude multilateral peacekeeping or conflict management interventions from our dataset. Biddle, Stephen, Jeffrey A. Friedman, and Stephen Long. (2012) Civil War Intervention and the Problem of Iraq. International Studies Quarterly, doi: 10.1111/j.1468-2478.2011.00705.x Ó 2012 International Studies Association International Studies Quarterly (2012), 1–14