The history ON Oklahoma refers to the history of the state of Oklahoma and the land that the state now occupies. Areas of Oklahoma east of its panhandle were acquired in the Louisiana Purchase of 1803, while the Panhandle was not acquired until the U.S. land acquisitions following the Mexican-American War.Most of Oklahoma was set aside as Indian Territory before the Civil War. It was opened for general settlement around 1890—the "Sooners" were settlers who jumped the gun.