Answer:
You could start by saying that Native Americans have been taking other Native lands for hundreds of years even before the Europeans came along, Native Americans followed war rules, which is to say that if you can take away someone's land, its fair game and fair, and if you fail to protect your land, its fair for the other people to take it. So really, Europeans were just following the rules the Native Americans already placed. Also, Native Americans frequently killed other people and tribes, which is just as bad, if not worse than having their freedom terminated. In terms of superiority, they wouldn't have to explain it, it would already be obvious. Think about if aliens came, and took over the earth, they would obviously be superior in one way or another.