To what extent do international factors affect domestic conflict processes? How do external conditions affect the state’s repressive capabilities and the opportunities for opposition groups to mobilize, launch an insurgency, and sustain it? This article argues that because state strength is limited by international boundaries, rebel groups often organize transnationally in order to evade repression. External bases, refugee communities, and characteristics of neighboring states are expected to increase the likelihood of civil war onset and continuation. Importantly, external mobilization is difficult for states to monitor and verify, a factor that exacerbates bargaining problems and increases the probability of armed conflict. These claims are tested through a quantitative analysis of civil conflicts from 1951 to 1999. Results suggest that weak neighbors, rival neighbors, and refugee diasporas contribute to rebellion and that conflicts endure longer when rebels have access to external bases.

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