When two cultures are incompatible with one another and they are in conflict, then "right" and "wrong" are essentially irrelevant. Only "winning" and "losing" matter.
Take your history back a few centuries if you want to talk about long cultural clashes/wars. The muslim invasion of Spain took place in 711AD and they stayed as occupiers until thrown out by a variety of factors in 1492. That's about 800 years of occupation. Simplistically, if the North American indigens hold out for another 600 years, they may yet get their land back, especially if we don't see this war for the long term danger it is...