In 1819 the Adams-Onís Treaty with Spain defined Oklahoma as the southwestern boundary of the United States. After the War of 1812 the U.S. government invited the Cherokee of Georgia and Tennessee to move into the area, and a few had come to settle. Soon intense white pressure for their lands, with the approval of President Andrew Jackson, forced the Cherokee and the others of the Five Civilized Tribes (the Choctaw, the Chickasaw, the Creek, and the Seminole) to abandon their old homes east of the Mississippi and to take up residence in what was to become the Indian Territory. Their tragic removal is known as the Trail of Tears. They settled on the hills and little prairies of the eastern section and built separate organized states and communities.
The Cherokee particularly had a highly Europeanized culture, with a written language, invented by their great leader Sequoyah, and highly developed institutions. Some of the Cherokee were slaveholders and ran their agricultural properties in the traditional Southern plantation pattern; others were small farmers. The Five Civilized Tribes clashed briefly with the Plains Indians, particularly the Osage, but they were for a time free from white interference, and they were able to establish a civilization that strongly affected the whole history of the region.
The troubles of the whites did not, however, long escape them, and the Civil War was a major disaster. Although no major battle of the war was fought in present-day Oklahoma, there were numerous skirmishes. Most Native Americans allied themselves with the Confederacy, but Unionist disaffection was widespread, and individual violence was so prevalent that many fled, leaving their farms to desolation.
As a punishment for taking the Confederate side the Five Civilized Tribes lost the western part of the Indian Territory, and the federal government began assigning lands there to such landless eastern tribes as the Delaware and the Shawnee, as well as to nomadic Plains tribes, who put up strong resistance before they were subdued and settled on reservations. The territory was plagued by lawlessness and served as a hideout for white outlaws. After the establishment of a federal court at Fort Smith, Isaac Parker became famous as the “hanging judge.”