This project examines the social, political, and economic transformations that shaped Choctaw nationhood following Indian Removal in the 1830s. Specifically, I argue that, unlike the other Five Tribes, the Choctaw Nation formed a more coherent sense of nationalism which included local education, commercial development, and political consensus which allowed them to remain a united people during the Civil War and Reconstruction. Whereas previous historians contend that a Confederate alliance was thrust upon hapless Choctaws who then joined lockstep with the Southern effort out of their shared interest in slavery, this dissertation demonstrates that Choctaws did not simply co-opt the Confederate cause. Rather, they selectively participated based on their own pragmatic national interests. I use the life of Choctaw Robert M. Jones as an interpretative lens to illuminate these various developments in the Choctaw Nation during the broader Civil War era. Jones, the wealthiest slave-owner in Indian Territory, owned six plantations, more than twenty trading stores, and as many as 500 slaves in the antebellum period. Despite his selective embrace of Southern cultural tenets, he remained an ardent Choctaw nationalist throughout his life. His experiences highlight the process of indigenous nation-building that transformed the Choctaw Nation during the broader antebellum and reconstruction eras. With this study, I reveal the importance of Native American agency and political sovereignty to the history of the Civil War west of the Mississippi and the broader narrative of Southern history.