A few thoughts:

-many settlers and colonies did actually purchase land from the 'natives', sometimes other tribes refused to recognize the purchase and there was conflict, sometimes other members of the selling tribe refused to recognize the deal, sometimes settlers expanded beyond the purchased boundaries.

-some of the conflict with the 'natives' was a result of agitation by the French, and other European powers against the colonies of their European rivals.

-The closest thing to a true genocidal campaign was carried out by the Republican administration after they defeated the Confederate States, continuing in their activities of corporate welfare/warfare in response to the interests of the Northern (and Midwestern) industrialists, first with the tariff and the war, then with clearing the west of natives to build the negative-value government subsidized railroads.