Between 1763 and 1773, North and South Carolina officials intensified their competition over their western backcountry when they attempted to resolve the boundary that had remained in question for decades. Historiography about this boundary has failed to recognize how common people in the Carolinas—Indians, colonists, and slaves—set the terms for the dispute and shaped the geography of early America. This boundary dispute offers a unique comparative glimpse of the Carolinas and exposes their most severe internal divisions—for North Carolina, the widespread Regulator movement that originated in disputes over western land, and for South Carolina, the heightened risk of slave revolts that accompanied the province's development. Catawba Indians occupied a central focus of the dispute, courted as an essential ally by South Carolina, while Cherokees hoped to halt the western expansion of both Carolinas. The boundary dispute determined the future of the diverging Carolinas, particularly in foreshadowing the tensions of state formation that manifested during the American Revolution. Indians, colonists, and slaves claimed their own spaces in between the imaginary lines of imperial power.