​​​​​​While much of the literature on interpersonal conflict explores the ways in which migrants passively affect the political behavior of locals, we know relatively little about foreign populations' capacity to play an active political role. In this paper, we argue that highly politicized migrants can use their political skills to influence the behavior of the population of the host countries. We explore this question by examining the exile of hundreds of thousands of Spanish Republicans to France following the Spanish Civil War. Using fine-grained data on the location of the refugees, we show that their presence is strongly associated with increased participation in the Resistance against the Nazis during World War II and with left-wing electoral support in the post-war period. Our findings demonstrate that migrants can be effective mobilizing actors within the host countries.