From my readings, it seems that the most feared plains indians were the Blackfeet (or Blackfoot). I’m surprised they weren’t mentioned.
E.g.:
“The Blackfoot of Montana and Alberta were once regarded as the most aggressive tribal people of the North American prairies.”
https://www.hfg.org/grant_summaries/blackfoot-traditional-models-of-aggression-and-healing/
The Sioux Uprising of 1862 in Minnesota pretty much deracinated the southern third of the state.