***They made peace treaties and then got screwed because of the settlers needing protection or land.***
In my reading it appears many of the treaties were never ratified by Congress so never went into force or law.
Still, they kinda got screwed over by the Fedgov. I've seen many documentaries, some liberal some factual, on how Sitting Bull, Crazy Horse, and Red Cloud were forced into what I would call "concentration centers". It was kinda sad for the Sioux who were not as barbaric as many other tribes, like the Apache, Comanche, Cheyenne, Zuni, Cree, Pawny, Iroquois and others earlier in the East. Yes, the Lakota Sioux massacred Custer's troops, but that was after trying to work with the US fedgov, IMHO.