Crossing the Line: When Neighbors Fight Rebels Across Borders

Abstract

Many rebels operate across borders, frustrating states which typically cannot cross borders in response. Yet states sometimes do fight rebels across borders, either with or without the consent of the crossed neighbor. When do states cross borders to fight rebels, and when do their neighbors accept this intervention? I develop a simple strategic model to answer these questions, drawing on insights from scholarship on borders and conflict as well as interviews with Ugandan border security officials. I test the empirical implications of the model using originally collected cross-national data on interventions and responses between 1989-2009. The results indicate that consent for intervention depends on neighbors' histories, rebel violence, and border geography. The results also cast doubt on the premise that states simply su er intervention when they must, as relative power plays a less consistent role in explaining intervention acceptance. I find evidence that the threat of resistance deters many cross-border interventions, but states' incentive and capacity to intervene provides an equal if not greater constraint.