Perhaps it was not intentional some of the time, perhaps most of the time.
There were many instances of genocide against the Indians, such as Schimmerhorn's massacre of the Arapahoes, and Custer's wiping out of a large number of Cheyenne.
The facts are these: go to Mexico, Peru, Colombia, pretty much any nation in South and Central America, and the Indian element in the population is obvious.
This is not true in the US, or Argentina or Uruguay, because Indians in those countries were mostly exterminated, some by disease, some by plan.