Answer: D. To reassure Eastern tribes that the territory was safe and thus encourage removal
Explanation: The disputes between the eastern and western tribes in the Indian Territory threatened removal. After that, there was a voluntary American Indian removal. The violence might make the eastern tribes unwilling to relocate. So, the US government built army bases to help maintain order (this is the US reaching into this area and saying, "If you move here, we will protect you"). I hope this helps.
