I think that within the subset of United States's aggression against the Native American population, there were many instances where fully integrated people were subsequently persecuted and eliminated. Some of it was at the "frontiers", yes. But some of it was shopowners, millers, brewers...people who had fully adapted and in fact thrived within the europeanized colonies and later states.
This was still happening in the 1950's and 60's as well, with the flooding of native lands in the Dakotas, etc, where fully "Americanized" communities were eliminated through forced relocation.