The answer is: manage land, reservations, for the Indian Tribes.
The main duty of the bureau of indian affairs is to increase the quality of life of the members of American Indians that live in united states.
In order to make up for stealing the Indian's lands in the past, American government granted the indian with several lands and reservations where they can live and build businesses. The bureau of indian affairs oversee the housing and the distribution of income from the businesses.
They did this in many ways. One important way was by signing treaties and not undergoing programmes of deradicalisation which as a consequence didn't decrease the desire of these people to maintain and even further their power following the World War 1.
