Determinants of Third Parties' Intervention and Alignment Choices in Ongoing Conflicts, 1946–2001

The decision to intervene in ongoing conflicts is one of the most difficult foreign policy choices states often face. Yet, studies of third parties' joining behavior have been rare and limited in several respects. First, they have explored only a subset of all interventions—military interventions. Second, they have concentrated on security-based determinants of intervention—power and alliance considerations—while underplaying other possible motivations behind the decision to intervene. Third, they have explored intervention and alignment choices as separate issues. This paper proposes a model of joining behavior that includes both security considerations and homophilous network ties as determinants of third parties' intervention and alignment choices. The model is tested on military and nonmilitary interventions data from Corbetta and Dixon (2005) for the 1946–2001 period. The results from a boolean logit estimation indicate that (1) the intervention decision is the result of both security-driven, pragmatic considerations and homophily between joiners and disputants; and (2) opposition to a party in a conflict is as important as a third party's social proximity to the side being supported.