Five Civilized Tribes and The Civil War

At the time of the Civil War, the Five Civilized Tribes owned most all of what became Oklahoma except for the Panhandle and Old Greer County. As punishment for siding with the Confederacy, the federal government took away the western half of their lands. These were the lands opened to settlers later in Oklahoma history.
They attempted to enter the Union as the state of Sequoyah in 1905, but instead joined Oklahoma Territory to become one state in 1907.