Why would Oklahoma tribes have been troubled about the black freedmen at the close of the Civil War?

The situation was quite complex. The State of Oklahoma was, before its separation from Texas, part of the original territory of the said state. Then it had been declared as Indian Territory where several displaced Native American tribes were relocated to such place during the Trail of Tears of the 1830s (Indian Removal Act).

At the onset of the Civil War, the Indian Territory was home to 55,000 native Americans, who owned 8,400 black slaves and about 3000 white Americans. Most Indians were thus pro-slavery and supported the Confederacy.

Therefore, as slave-owners they resented the destruction of the status quo and the abolition of their priviledged status and the subsequent liberation of their black slaves without any form of monetary compensation.