Foreign military interventions are correlated with longer civil wars, yet existing explanations for this association remain inadequate. One influential argument claims that outside states prolong internal warfare by introducing objectives that are extraneous to the conflict at hand. A more compelling extension of this argument is that intervening states forge alliances with local combatants, and contention among these local combatants creates friction among intervening states and opens the door to additional combatants. Such dynamics lengthened the civil war in Yemen that erupted in 2012–13. Exploring the shifting patterns of antagonism and alignment that accompanied intervention in this particular case improves our general understanding of the mechanisms that increase the duration of internal warfare.

外国军事干预与更长的内战有关，但对这种关联的现有解释仍然不充分。一个有影响力的论点声称，外部国家通过引入与当前冲突无关的目标来延长内部战争。这个论点的一个更令人信服的延伸是，干预国家与当地战斗人员结成联盟，这些地方战斗人员之间的竞争会在干预国家之间制造摩擦，并为更多的战斗人员打开大门。这种动态延长了也门在 2012-13 年爆发的内战。探索在这种特殊情况下伴随干预的对抗和结盟的变化模式，可以提高我们对增加内战持续时间的机制的总体理解。