The area that is now Oklahoma was once a place called Indian Territory. Beginning in the 1800s, the U.S. government designated the land in the Great Plains as a place where it could force indigenous peoples in order to make room for American settlers as they pushed west. All of the routes on the Trail of Tears led to what became Oklahoma.
During the Civil War, some of the tribes based in Indian Territory made alliances with the South rather than the North. These tribes had roots in Southern states like Georgia and Florida, and they owned slaves and grew cotton.
After the war, the U.S. government penalized the tribes that had aligned with the Confederacy, forcing them off their land in Indian Territory. This left an area of roughly 2 million acres — about half the size of Connecticut — suddenly empty. This patch of Indian Territory became known as the Unassigned Lands.
The Unassigned Lands would become a source of fascination for settlers in the surrounding areas, which Sam Anderson chronicles in his book Boom Town. The book explores the history of Oklahoma City — now located in the middle of what used to be the Unassigned Lands — from its bizarre founding to the present day.