Alvin Josephy said that reservations and the continuing attachment to land they afforded have been instrumental in the survival of American Indian cultures. Reservations were, for the most part, diminished versions of ancient tribal landscapes, but however diminished, they were pieces of those larger lands—particular lands that had sustained particular tribal peoples for millennia.
Policies of removal and assimilation have of course taken many—most—Indians away from ancestral grounds over the last five centuries. There are now more urban Indians than rural Indians, and tribal enrollments are covered in confusion, with each tribe establishing its own enrollment requirements, and individual Indians finding themselves descendants of many tribes and sometimes living on a reservation where they are not, maybe cannot be, enrolled.
There have of course been movements of indigenous tribes through history, brought on by famine, weather, natural catastrophe, intertribal warfare and European colonization. Alvin Josephy began his landmark book on American Indians, The Indian Heritage of America, published in Read The Article