Abstract
<jats:p>How does migration enforcement in transit countries affect security? As border externalization — where migration destination states pressure transit countries to intensify migration enforcement — becomes a central tool of migration governance, its downstream effects remain poorly understood. We theorize that border externalization can increase violence along migration routes by creating incentives for high capital criminal organizations to enter and control the migrant sector. We evaluate this theory by studying the 2019 Migrant Protection Protocols (or “Remain in Mexico"), which pushed Mexico to crack down on migration along its own southern border. Using original data on migration routes, we show that Remain in Mexico increased homicides along migrant routes, and is associated with increased cartel presence and cartel exploitation of migrants. By tracing the consequences of migration policy beyond the borders of destination states, this study shows how externalized border enforcement can undermine security.</jats:p>