Tribes stole land from other tribes.
Shhhh...keep that quiet. People aren't supposed to know that many Indian tribes were stone killers who took i.e. stole the land of other tribes while slaughtering many of them.
One of the most shameful incidents in our nation's history concerned the Sac Indians and Chief Black Hawk of whom a number of parks in my area are named after.
In 1832 BH's people were starving, so they left their reservation looking for food. They were chased by federal troops and they ended up near the Mississippi River not too far south of where I grew up.
They were attacked by the federal troops who caught them and started shooting everyone including women and children.
Some Sac Indians tried to escape across the Mississippi. Unfortunately, waiting for them, along with federal gunboats, was their arch enemy, the Sioux, who finished the job the federal troops started slaughtering as many Sac Indians as they could.
Neither side is blameless in our nation's history as far as cruelty and slaughter.
But to accuse the federal gov. of all the Indian problems and cruelty while ignoring the bitter feuds/wars between many Indian tribes does a disservice to history and the truth.