Hi there -- there's always more to be said on this topic, but perhaps these older posts featuring u/snapshot52 describing in detail the genocides of the Native American population will be a place to start:

https://www.reddit.com/r/AskHistorians/comments/6kywre/monday_methods_american_indian_genocide_denial/

and

https://www.reddit.com/r/AskHistorians/comments/6mg3j3/monday_methods_american_indian_genocide_denial/