We propose that emigrants affect the likelihood of civil war onset in their state of origin by influencing the willingness of individuals to join rebel movements and the probability that the state and rebels will be unable to reach a mutually acceptable bargain to avoid conflict in three ways. First, migrants communicating with actors at home facilitate valid comparisons between the effects of policies in the home state as compared to policies in the host state enacted on a similar group, creating new motivation to join collective challenges against the state. Second, migrants send remittances, providing resources that can be used in collective challenges that are particularly difficult for states to anticipate, making the outbreak of conflict more likely. Finally, migrants publicize information about conditions in their home state while living in the host state, reducing home government uncertainty such that conflict is less likely to occur. We test these hypotheses on an international dataset and find support for each of our predicted mechanisms.