Civil War in the Shadow of Intervention

I argue that expectations of third-party intervention shape the decision to start a civil war. To assess the claim, I develop a theoretical model of onset and intervention and a subsequent statistical approach built on a predictive measure of intervention. Intervention expectations improve model fit and out-of-sample performance relative to a standard model and a similar model in the literature. Not all interveners are the same: major powers, rivals, neighbors, and coethnics play unique and quantifiable roles. More interestingly, intervention expectations did not play a uniformly important role throughout the second half of the 20th Century, and the end of the Cold War appears to have brought on a new intervention-onset process. Remarkably, intervention expectations seem to explain away the well-known effect of population on the onset of violence. These results suggest that the shadow of intervention looms large in powerful but nuanced ways. ∗Thanks to the Kroc Institute for International Peace Studies, W. Allen Wallis Institute of Political Economy, the star lab, and the Institute for Humane Studies for generous support. Thanks in particular to Curt Signorino for guidance. This paper has benefitted from discussions with Jeff Arnold, Quintin Beazer, Inken von Borzyskowski, Mike Colaresi, Tyson Chatagnier, Kevin Clarke, Casey Crisman-Cox, Amanda Driscoll, Kevin Fahey, Mark Fey, Nisha Fazal, Hein Goemans, Phil Henrickson, Gary Hollibaugh, Brenton Kenkel, Hye-Sung Kim, Bethany Lacina, Jeff Marshall, Will Moore, Jonathan Olmsted, Kai Ou, Matt Pietryka, Amy Pond, Pat Regan, Chris Reenock, Brad Smith, Mark Souva, Randy Stone, and Susanna Supalla. It has also benefitted from presentations at the Midwest Political Science Association meetings and the Peace Science Society (International) meetings. Despite all this amazing support, the usual caveat applies. We often invoke third party intervention as a potential channel for civil order, as it may deter violence before it starts. But, it also might enable violence by offering opposition groups a lifeline or brutal dictators a safety net. My goal in this paper is to find out how, if at all, the shadow of intervention so affects the onset of civil war. Precisely, I provide below (1) a general, unified framework linking onset and intervention; (2) a statistical approach directly related to the theory; and (3) a predictive measure of intervention expectations. I then use these tools to argue for and provide evidence supporting the importance of the shadow of intervention. Previewing the results, a fair read of the evidence suggests the following: 1. Most fundamentally: the shadow of intervention matters. Intervention expectations significantly improve fit over a standard model. Lest the reader worry that the result only reflects overfitting, expectations also improve out-of-sample predictive performance (see Table 2, p. 18). On this second point, intervention expectations are among the most important predictors for onset (Table 5, p. 27), playing both direct and indirect (i.e. interactive) roles in ways that other common predictors do not. 2. Echoing Thyne (2009): accounting for the international environment allows for a more dynamic view of onset. Many country-level predictors of civil violence remain fixed over time (e.g. mountainous terrain, at least on our time frame! ) or evolve slowly (e.g. population), often in a single direction. Conversely, intervention expectations ebb and flow (Figure 5, p. 21), which in turn lets them improve performance around the onset of violence (Table 3, p. 22). If (say) low incomes provide the kindling for war, then the international environment may shift quickly enough to create the spark. 3. Relatedly, the international environment did not play a uniformly important role in the second half of the twentieth century, and the baseline and internationalist models performed similarly during the 1940s–1950s. A spate of civil wars from the mid-1970s to the late 1980s seems to be well-explained by a decrease in the likelihood for intervention by superpowers (Figures 4 and 5, pp. 20–21). Intervention expectations played an especially important role after the end of the Cold War, reinforcing a point made by Kalyvas and Balcells (2010) (that the international system matters) but from a very different angle. 4. Strikingly, the internationalist approach calls into question the influence of long-cherished country-level predictors. The results severely weaken