The region, as one of the purchase's most attractive parts—because of trade opportunities—might well have become one of its first states; but it was in fact the last. Because of hostile Native Americans, Spanish intrigue, the mislabeling of the region's treeless plains as the Great American Desert, and the pressure for removal of the Native Americans from the settled East, the U.S. Congress in 1828 reserved Oklahoma for Native Americans and required all others to withdraw. By 1880 more than 60 tribes from other areas of the country—in the 1830s, such Eastern groups as the Creek, Cherokee, and Choctaw, and, in the 1870s, such Plains Indians as the Cheyenne, Arapaho, Kiowa, and Comanche—had been forcibly removed to Indian Territory, where they joined local groups such as the Wichita and Kansa. Among both the original inhabitants and the newcomers, some were sedentary, peaceful, agricultural, and Europeanized (even to the point of owning slaves of African descent), while others were migratory and eager to fight in defense of their land and other interests. The newly defined Indian Territory consisted of five republics, or nations, with fixed boundaries, written constitutions, courts, and other governmental apparatus similar to those of the Eastern states. The major difference was that in each republic all land was held jointly or in severalty by an individual tribe. The first major threat to these governments came when, as former allies of the South during the American Civil War (1861–65), they were placed under military rule during the Reconstruction (1865–77) period.As the historian of the American West Robert Utley has pointed out, US Indian policy was largely militarized in the post-Civil War period, which meant the Army that was heavily conditioned by the combat of the Civil War was largely in charge of it.
The Reconstruction treaties required, among other things, land cessions to former slaves, the resettlement of additional outside tribes, and railroad rights-of-way. Although a scheme to colonize free blacks in Oklahoma never materialized, the weakness of the Native American governments encouraged non-Native Americans from adjoining states to trespass. Thus, the territory again became an embattled refuge for Native Americans and an even greater cultural hodgepodge of ethnicities. [my emphasis]
After famously marching through Georgia, and less famously marching through South Carolina in a similar fashion, William Tecumseh Sherman served as commanding general of the Army in 1869-1884. His service in that role was heavily concerned with Indian policy. His contributions in that role were less historically beneficial than those during his Civil War service.
Slavery also existed in the Indian Territory of present-day Oklahoma in antebellum times:
... slaves made up a significant percentage of the population in Indian Territory (present-day Oklahoma) and therefore must be included in accounts of the history of the Five Tribes (the Choctaws, Chickasaws, Creeks, Cherokees, and Seminoles). Inexact yet revealing population statistics illustrate the magnitude of the peculiar institution in the slave holding nations of Indian Territory. At the outbreak of the Civil War a minimum of 10 percent of the Creek population was enslaved. Among the Choctaws at least 14 percent of the population was in bondage, and among the Cherokees the number may have surpassed 15 percent. On the far end of the spectrum, the Chickasaws enslaved fully 18 percent of their population. The Seminoles represent a special case. Although by one contemporary estimate nearly 30 percent of the population was enslaved, the line between slavery and kinship was less clear in this nation than in any other in Indian Territory. In total, the enslaved population in the Five Tribes numbered perhaps as many as ten thousand. [my emphasis]White racial hatred and violence are scarcely new to the State of Oklahoma. Gregory and McNamee write:
Ethnic tensions between Oklahomans of European (“white”) and African (“black”) descent (and sometimes between members of these groups and Native Americans and Hispanics) were commonplace during the early years of statehood and were manifested as isolated lynchings and propaganda against African Americans. These tensions culminated in race riots in 1921 in Tulsa, during which some 35 city blocks in the African American community were destroyed and several hundred people were killed. [my emphasis]Dave Neiwert discusses the 1921 riots in The Kinds of Things You Might Learn in an Oklahoma AP History Course Orcinus 02/20/2015.