Why foreign military interventions prolong civil wars: lessons from Yemen

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.