The native Americans were not able to defeat the Americans and so the native Americans rebellion lost its impetus

Yes, it is true that the native americans were not able to defeat the americans and the native Americans rebellion lost its impetus but what is your question?

The statement you have written is indeed true, as shortly after the Westward Expansion, the Native Americans were completely powerless to the Americans, leading to it's collapse and the population going down and down as the Americans went up and up.