Most early history concerning Native Americans has been written by white army officers or political figures. Needless to say how bias it was. The truth of the matter is that the white's wanted the Indian's lands and intended to acquire them by any means possible. And once those lands were acquired the Indians had to be removed to keep them safe.
As has been evidenced here the military and government used any and all means to justify their actions in acquiring those lands. The government made over 370 treaties with the Native Americans and broke every one of them.