A theory of competing interventions by external powers in intrastate conflicts: implications for war and armed peace

This paper presents a game-theoretic model of competing interventions in civil conflict. We analyze the conflict between an incumbent government (as defender) and its rebel group (as attacker) when the two parties receive military support from different external powers. In contrast to the traditional analysis of non-competing or biased intervention by a single third party, we first show how competition in external powers can strategically alter the outcome of the two-party conflict and then identify the conditions under which the defender launches an effective strategy to deter the attacker. We find that (i) when the stakes that the competing external powers have in their respective supported parties are equivalent, the amounts of military support endogenously offered by the external interveners are comparable. The government’s deterrence strategy is ineffective, and the fighting persists despite the warring parties’ valuations for political dominance being asymmetric. (ii) when the external power that supports the government has a higher stake than the competing external power that supports the rebel group, the government’s arming allocation can deter the rebellion. (iii) These results have implications for multi-power interventions so that the equilibrium outcome can be ‘armed peace’ or a prolonged war as observed in civil conflicts.