Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Political Science


Why do individuals take the extraordinary risk of traveling abroad to fight, and potentially die, in another country's conflict? This dissertation compares the motivations behind the U.S. citizens who fought on behalf of the International Brigades in the Spanish Civil War (1936-1939) and the Tunisian citizens who fought on behalf of the Islamic State of Iraq and Syria (ISIS) in the Syrian Civil War (2011 - present). The study relies on personal narratives of individual foreign fighters collected through twelve weeks of archival research at the Tamiment Library in New York City and the Ernest Hemingway Archives in Boston dedicated to U.S. foreign fighters and fifteen weeks of field research in Tunisia conducting interviews and examining interview and focus group data on Tunisian foreign fighters to understand the competing motivations driving individual decisions to travel and fight for a foreign cause.

This dissertation's findings suggest that a robust understanding of the foreign fighter phenomenon must, by necessity, draw on multiple theories and scholarly literatures. Three factors, social networks, collective identity, and sacred values, are significant across both cases, suggesting that they are necessary factors driving the foreign fighter phenomenon. A fourth factor, structural grievances, was significant in explaining the case of Tunisian foreign fighters to ISIS but not U.S. foreign fighters to the International Brigades, suggesting that the finding is not robust, but is nevertheless one that is ripe for future research. Personal grievances and economic incentives were not significant factors in either case. These results potentially establish foreign fighting as an act that is distinct among different types of collective action, with implications for both academics and policymakers.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.