While it’s true that there was inter-tribal warfare before the European invasion, it was disease (sometimes spread intentionally and sometimes just by the settlers’ poor sanitary standards), warfare and outright massacres, relocation marches, and deliberate starvation perpetrated by the Europeans and then the US government which reduced the indigenous population from the pre-contact 20 million to 250000 by 1900. At the time of this film’s setting, the US policy was definitely extermination of the native identity, either by assimilation or massacre when they resisted. This is not a matter of debate: you can read for yourself both the government edicts and the historical records.

Oh shut up. The Indians had been slaughtering each other for 1000 years before the white man showed up in the continent.