How do migrants decide when to leave? Conventional wisdom is that violence and economic deprivation force migrants to leave their homes. However, long-standing problems of violence and poverty often cannot explain sudden spikes in migration. We study the timing of migration decisions in the critical case of Syrian and Iraqi migration to Europe using an original survey and embedded experiment, as well as interviews, focus groups, and Internet search data. We find that violence and poverty lead individuals to invest in learning about the migration environment. Political shifts in receiving countries then can unleash migratory flows. The findings underscore the need for further research on what migrants know about law and politics, when policy changes create and end migrant waves, and whether politicians anticipate migratory responses when crafting policy.