D. As "Indian Territory" for thousands of Native Americans displaced from the southeastern United States.
Explanation:
Most of Oklahoma was set-aside as "Indian Territory", as the United States government wanted to move the Native Americans from their tribal lands in order to expand.
The Indian Removal Act was passed in 1830, which meant the Native Americans had to move from their homes and go to the territory that was for them in Oklahoma. They obviously did not want to go, but many knew that they would not stand a chance against the United States government.
Years later, some of the Cherokee Natives were still there and were not moving, this caused the United States military to get involved and had to force them out. Native Americans were walked at gunpoint all the way to Oklahoma, this walk is known as the Trail of Tears. Thousands of Natives died of diseases, starvation, and weather conditions during this walk.
