Which armed organizations form coalitions despite the inherent difficulties of cooperation in civil wars? We introduce the concept of tacit coalitions, which pertains to strategic and informal coalition behavior between civil war actors to address this puzzle. Our theoretical model of coalition behavior takes in theater-wide conflict behavior to allow for predictions that coalitions are more likely to form. It provides novel insights into the way military synergies within potential coalitions affect the trade-off between pooling resources and worrying about the division of gains. The empirical section finds considerable support for our theoretical argument that actors are more likely to engage in tacit coalition behavior (1) if potential coalitions are power balanced, (2) if joint capability of potential coalitions is not too high, and (3) when coalitions can unlock synergies. In addition, it produces evidence for the important role of geography and ethnic ties in generating military synergies.

中文翻译：

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谁加入谁战斗？解释内战参与者之间的默契联盟行为

尽管在内战中存在合作的固有困难，哪些武装组织结成了联盟？我们引入了默契联盟的概念，它涉及内战参与者之间的战略和非正式联盟行为，以解决这个难题。我们的联盟行为理论模型考虑了战区范围内的冲突行为，以预测联盟更有可能形成。它提供了关于潜在联盟内的军事协同作用如何影响集中资源和担心收益分配之间的权衡的新见解。实证部分为我们的理论论点提供了相当大的支持，即行动者更有可能参与默契的联盟行为（1）如果潜在联盟是权力平衡的，（2）如果潜在联盟的联合能力不太高，(3) 联盟何时可以发挥协同作用。此外，它还为地理和种族关系在产生军事协同作用中的重要作用提供了证据。