It was inevitable that a small number of relatively primitive people, occupying an entire continent, would eventually be displaced by a more advanced civilization. Had it not been Europeans, it would have been someone else. Certainly, before the arrival of white Europeans the native Indian tribes had no qualms about wiping out their neighbors and taking their land, often taking (gasp) slaves in the process. They also did things, like stampede entire herds of buffalo off cliffs in order to take only a few of them, that the PC multiculturalists would have you believe are the exclusive domain of the "wasteful" white settlers.
I know that in many ways American Indians were treated shamefully during those times, but the full story was much more complex than the "pure, innocent Indians versus the evil, greedy Europeans" tale that is told by liberals.