The treaties of 1866 meant the Indians no longer controlled their own destiny. Why?

The Indians no longer owned their own destiny, because their sovereignty was restricted by U. S. government and their assets were open to others people exploitation.

Explanation:

The Indians no longer owned their own destiny, because their sovereignty was restricted by U. S. government and their assets were open to others people exploitation.

Most destructive feature of such treaties were land loss. For many other Tribes, the Five Tribes had to surrender the western half of Oklahoma as a camp for refuge

Because the Indian land was being sold to settlers for a cheap price. The Indians were moved to set aside land (reservations) where they were not happy. These lands were very poor for agricultural purposes and did not provide much opportunity for the native Americans.