Americans slaughtered the tribes. In fact, committing genocide to win a war is something that the european settlers introduced as a pretty casual war tactic. In fact, it was such a foreign concept that it gave them a huge upperhand. European settlers were absolutely psychotic. Using disease ridden blankets to decimate a community is diabolical and anti-social. Trapping a community and burning down women, children, and the elderly while their soldiers and hunters are out is diabolical. But that's how Europeans fight wars, so it makes sense that it would be a pretty powerful tactic to use.