Which states intervene in which wars, and what intervention strategies do they choose? These are the questions Aysegul Aydin addresses in Foreign Powers and Intervention in Armed Conflicts. Her answers revolve more around economic connections between belligerents and third parties, than around the traditional power politics concerns more commonly found in intervention studies.

Aydin does not reject realist arguments about interventions; indeed she finds consistent support for the realist expectation that major powers are likely to intervene regardless of other contextual variables. However, she stresses instead the importance of economic ties between would-be interveners and belligerent states. Her liberal economic theory centers on motivations for intervention among and constraints against would-be interveners. Both the motivations and the constraints are internal to the potential intervener, and hence fall within the purview of liberal IR theory. According to Aydin, interveners are motivated by a desire to protect the commercial and financial interests of their domestic economic actors in belligerent states. Thus, she anticipates that interveners will be states with disproportionately high levels of trade, foreign direct investment, and/or preferential trade agreements with belligerent states. Constraints arise from domestic political arrangements within the would-be intervening states. For example, leaders of democracies are more constrained from intervening to protect domestic constituents because they have to appeal to broader portions of the population than do the leaders of non-democracies. Aydin thus offers a hierarchy of likely interveners, with non-democratic third parties conducting extensive trade and investment with belligerents the most likely to intervene.

The argument is evaluated in a pair of quantitative chapters and a third qualitative chapter featuring narrative case studies of American intervention decisions. The statistical analyses are notable both for the sophistication of the estimation techniques used, and for the originality of combining heretofore separately analyzed datasets. The American cases are particularly apt for investigation, because the United States is one of the most frequent interveners in the international system. The reader comes away convinced that economic factors loom large in decisions to intervene. This is a valuable and original contribution.

Aydin’s book is particularly notable for the rare unification of analysis of interstate conflicts and civil wars. That is, she analyzes her theory of intervention in both militarized interstate disputes and in civil wars. While a variety of scholars have pointed out that the standard bifurcation of IR conflict studies into discreet inter- versus intrastate areas of investigation is artificial, it is still extremely rare for investigators to include both interstate and intrastate conflicts in one study. Unifying analysis of both types of conflicts helps critique the unsubstantiated claim that they truly are different “types” of conflicts, and also increases confidence in Aydin’s theoretical argument because she finds that strong economic ties between belligerents and third parties make interventions more likely in both inter- and intrastate conflicts. Her theory thus has a larger empirical domain than the competition which, again, tends to look only at interstate conflicts or only at civil wars. I very much hope her example will be emulated by scholars following in her footsteps.

One of the main findings of the book is particularly intriguing. In Chapter 4, Aydin finds and reports that economic ties make specifically military interventions more likely in interstate conflicts. But in Chapter 6 she finds and reports that economic ties make specifically economic or diplomatic interventions more likely in civil wars. In both instances economic ties increase the odds of intervention, so the unified framework is supported. But, the strategies of intervention vary across the two “types” of wars. Aydin suggests this difference may be caused by the fact that interstate conflicts tend to be quite short, limiting the down-side risks of military interventions. Civil wars, however, tend to drag on far longer than do interstate conflicts, and thus interveners have to be more cautious about involving themselves militarily because the costs will likely be far higher. While this is a plausible explanation, it does not exhaust interest in this finding. This is because in Chapter 1 (specifically Table 1.1 on page 3) Aydin reports that the most frequent type of intervention in inter-state conflicts is diplomatic (71 percent) and the most frequent type of intervention in civil wars is military (59 percent). Thus, not only do economically interested states vary their intervention strategy across inter- and intra-state conflicts, but they do so in directly opposite fashion to how the average or normal intervener intervenes. That is, the most frequent type of intervention in civil wars is a military intervention. But the economically motivated interveners are disproportionately likely to intervene non-militarily in civil wars. Similarly, economically motivated interveners run contrary to the norm because they favor military interventions in interstate conflicts whereas most interveners (the vast majority, actually), favor diplomatic intervention. The question then is: Why do economically motivated interveners differ so much from interveners in general? This question is unanswered.

It may be that economically motivated interveners differ from interveners in general because their interests in the belligerent states are stronger than those of general interveners. In Chapter 2 Aydin writes about interventions in different phases of conflicts: pre-conflict, conflict, and post-conflict. Figure 2.1 (p. 25) indicates that pre-conflict interventions are intended to prevent conflict, and post-conflict interventions are intended to reconstruct the country, presumably to make recurrent conflict less likely. Although Aydin does not theorize about, nor does she analyze pre- or post-conflict interventions, it seems plausible that economically motivated third parties are perhaps the most likely to intervene in these pre- and post-conflict phases. A more developed theoretical argument that incorporated these other two phases would surely represent a step forward from the argument presented here, and might help us understand better why economically motivated third parties intervene differently than do other interveners.

This is an interesting book. Analysts of both interstate conflict and of civil war will find much to think about within it. The focus on economic motivations and domestic political constraints places it squarely within the liberal IR theory tradition, but is nonetheless original in intervention studies. That the theory does not discuss strategic interaction among belligerents and potential interveners, nor among potential interveners, will be disappointing to those favoring more current IR theorizing than the traditional debates between liberals and realists. It is likely that very different hypotheses would emerge if such considerations were taken into account. I look forward to seeing how Aydin and future scholars build on this work, in hopes that unified analyses of civil and interstate conflicts become the norm and in hopes of solving new theoretical puzzles such as that highlighted above.