What messages do insurgencies use to recruit foreign fighters? As recent events from Afghanistan and Iraq to Yemen and Somalia demonstrate, foreign fighters represent a significant concern in counter-insurgency planning and a growing challenge to basic concepts of sovereignty. Yet transnational insurgencies are not merely a contemporary phenomenon, nor one limited to Islamists. How have recruiters in various conflicts elicited costly collective action in distant wars where foreigners would seem to have had no apparent grievances or interests at stake, and in which empirical evidence also sugge ... More

What messages do insurgencies use to recruit foreign fighters? As recent events from Afghanistan and Iraq to Yemen and Somalia demonstrate, foreign fighters represent a significant concern in counter-insurgency planning and a growing challenge to basic concepts of sovereignty. Yet transnational insurgencies are not merely a contemporary phenomenon, nor one limited to Islamists. How have recruiters in various conflicts elicited costly collective action in distant wars where foreigners would seem to have had no apparent grievances or interests at stake, and in which empirical evidence also suggests recruits were offered little in the way of material incentives? To answer this question, this study presents a data set of transnational insurgents and a typology of foreign fighters. It then offers comparisons across four disparate case studies: The Texas Revolution (1835-36), the Spanish Civil War (1936-39), the Israeli War of Independence (1948-49), and the Afghanistan War (1978-1992). The data indicates that transnational recruitment occurs when local insurgents attempt to broaden the scope of conflict to increase their resources and maximize their chances of victory. However, due to their lack of resources, they typically must motivate outsiders to join them for reasons other than material gain. They therefore overcome collective action barriers by framing participation in conflicts as a necessary defensive mobilization against existential threats to transnational ethnic, religious, or ideological groups they share in common with the recruits. This consistent recruitment pattern likewise suggests common dissuasion and disruption strategies available to counter-insurgency planners.