We examine how violence affects migration flows and, crucially, how it reshapes the strength of migration networks -- measured by the intensity of migration between areas, accounting for the fact that some routes become more prominent or fade over time -- an aspect traditional studies overlook. Using a novel network algorithm and Mexican census data from 2005 to 2020, we first quantify changes in the strength of domestic and international migration networks across all Mexican municipalities. We exploit variation in local homicide rates, using exogenous fuel price increases and municipalities' proximity to oil pipelines as instruments, to estimate the causal impact of violence on migration. During our study period, following intensified government crackdowns on drug trafficking organizations, many criminal groups fragmented and turned toward large-scale oil theft, driving sharp increases in violence in areas with oil pipelines, particularly when fuel prices rose. The findings show that rising violence increased emigration flows, predominantly within Mexico, and strengthened the intensity of emigration networks both domestically and toward the United States. Although violent municipalities continued to receive new residents, the rise in emigration was larger. Increasing homicide rates led to at least an additional 1.12 million people emigrating domestically and 50,200 fewer Mexicans returning from the United States. Violence also eroded regional connectivity, causing a long-term decline in daily vehicle traffic on highways linking violent areas to the rest of the country.