Beyond Mountains is a longue durée history of fugitivity, survivalism, and insurgency in the heart of North America. Reconstructing the worlds of mobile and multi-ethnic communities, Max Flomen details generations of rebellious collaboration and anticolonial reinvention across the borderlands of northern Mexico and the American Southwest, arguing that militant Indigenous factions, often religiously inspired, waged a protracted struggle against the Spanish, French, Mexican, and U.S. empires by collaborating with the mostly forgotten figures of the frontier underworld—vagabonds, apostates, fugitives, and captives. Beyond Mountains employs the concept of marronage, broadly defined as escaping colonized spaces to form new communities, to examine how converging motives and close coordination allowed the dispossessed of the Southwest borderlands to create a revolutionary form of sovereignty. Moving back and forth from flight to confrontation, these borderlands insurgents defied policies of confinement, discrimination, and exploitation by infiltrating settlements, manipulating information, and extracting resources in pursuit of their autonomy. Where previous historians have viewed anticolonial rebels through isolated incidents, Flomen treats them as a centuries-long movement against imperial control. By taking seriously the networks of small-scale, anti-state societies, Flomen renders legible the coalitions that had little tolerance for the dictates of colonial authorities.