Indian Territory was the lands set aside within the United States for the use of Native Americans. The Indian Territory had its roots in the British Royal Proclamation of October 1763, which limited white settlement to crown lands east of the Appalachian Mountains. This was reduced under British administration and after the American Revolution further until it included only the lands west of the Mississippi River.
At the time of the American Revolution, the Native American tribes had long-standing relationships with the British, but a less developed relationship with the American rebels. After the defeat of the British, the Americans twice invaded the Ohio country and were twice defeated. They finally defeated the Native Americans at the Battle of Fallen Timbers in 1794, imposing the unfavorable Treaty of Greenville, which ceded most of what is now Ohio and part of what is now Indiana to the United States.
In time the Indian Territory was gradually reduced to what is now Oklahoma and, with the organization of Oklahoma Territory, the eastern half of the state. With statehood in November 1907, Indian Territory was extinguished. Many Native Americans continue to live in Oklahoma, especially in the eastern part.
In the 1830s the Indian Territory served as the destination for the policy of Indian Removal started by President Andrew Jackson. The end of the Trail of Tears was what is now Arkansas and Oklahoma. There were already many tribes living in the territory, as well as whites and escaped slaves.
The Five Civilized Tribes set up towns such as Tulsa, Tahlequah, Muskogee, etc., which often became some of the larger towns in the state. They also brought their African slaves to Oklahoma, which added to the African-American population in the state.