A great deal of that was done in boarding schools in the late 1800s. The children were not permitted to speak their native tongues.
When I visited the Custer battlefield (Little Bighorn) some years ago I overheard a conversation about how the Crow Indians were told they had to speak English. I think that was by church leaders. The Crow were allies of the Seventh Cavalry in the war against the Sioux in 1876.