The Indians fought us in even more nasty ways than we fought them, but that part of the history has been cleansed.
This isn't some racist genocide as Native American activists have portrayed it. The settlement of the American frontier was just another episode of the clash between a hunter/gatherer civilization, which requires huge amounts of land to support a small population, and agriculturalists, who support far larger numbers but limit the herds. This clash has been going on ever since domestic agriculture was invented in Mesopotamia thousands of years ago. The agriculturalists always win.
(Please, I know there were some Native American agriculturist tribes, but they occupied a very small part of the American landmass.)
The Indians actually farmed quite extensively. Plus, the Indian farmers should have prevailed if your thesis were to be true(considering the time span they were there).
There is another more serious problem with your thesis, many places were converted from nomadic to farming but the people were still the same.
The Indians are gone from quite large population estimates. They are limited to reserves.
I did not state that the Indians did not fight just as bad or worse, in fact there is evidence that Caucasians were in North America (a 7000 year old skeleton has been found and there are stories of a red haired tribe). These Caucasians were wiped out.