It’s been several years since I read about this.
East of mid-MT. Seems like it was between two buttes or by a butte.
Crow on one side.
Probably Sioux on the other, but might have been a different tribe.
Pre Civil War.
Don’t forget the Aztecs and Mayans.
They had some big battles. Mexico is in North America...
That would have to have been a big battle involving thousands.
There were several massacres on the northwest frontier during the Tecumseh period circa 1810 and in the south for and against the cree (or creek) indians that involved many hundreds of killed.