In 1828 Congress designated the land that would become Oklahoma as Indian Territory. White settlers were required to leave, and a number of tribes from the East and South were forcibly moved into the area from their ancestral lands. Chief among these were the Five Civilized Tribes – the Cherokee, Choctaw, Chickasaw, Creek and Seminole – who allied themselves with the South during the Civil War. Following the war, the US government looked upon these tribes as defeated enemies. This animosity combined with increasing pressure to open up the Indian Territory to white settlement prompted the first land rush in 1885, a second followed in 1889.
Source: The Oklahoma Land Rush of 1893