How do people behave when confronted with uncertainty and violence? This dissertation examines how Central American migrants cope with escalating violence in transit and how these coping tactics reshape the social landscape of transnational routes. From villages in El Salvador into Mexico and through the United States, the sustained practice of migration informs behavior along a dangerous route, not only through social networks, but also by carving a transit political economy and transnational imaginary. Migration decisions are rational, but must be viewed as an ongoing process of learning constituted by information gathering, imagination and improvisation en route. As people move along these routes, migrants and citizens improvise new identities, shifting national, racial and gendered boundaries. The ethnographic framework of this dissertation elucidates the implications of this process for the governance of states through which transnational flows pass. The attempt to impede these flows within the territory of transit states, like Mexico, has not only thickened borders and policing; it has extended the social ambiguities and uncertainty of the borderlands, inviting the Hobbesian anarchy of the international system into the domestic domain of the state. Thus, this dissertation points to how migrants and citizens share the catastrophic human security consequences of migration policing.