This essay focuses on the borderlands of Mexico and the United States in the decades following the Mexican-American War. There, American, Apache, Comanche, and Mexican inhabitants came into contact with one another and their distinctive and sometimes conflicting understandings of sovereignty led to significant discord. In different ways, Mexico and the U.S. sought to assert control over part of these borderlands, which included restricting the movement of outsiders within their territory. Apache and Comanche peoples, on the contrary, regarded free movement across the region as “irrevocable.” The increasing American population both provided demand for livestock that drove indigenous raids into Mexico and curtailed access to land and resources, promoting migration across the border and making it exceedingly difficult for Mexico to assert sovereign control over northern territory.