And the Lakota Sioux took it from the Cheyenne tribe by arrow point only 100 years prior to that. So yea, the Sioux had the land stolen from them by force, but they stole it by force themselves before that. And by this point, the US has controlled the land longer than the Sioux ever did.

On the other hand, the US did have a formal treaty with the Sioux that granted them the land which the US willfully broke when gold was discovered.