As Neal Degrasse-Tyson pointed out once: What is indigenous, when do you start the clock and say from now on everyone who is in a place is indigenous? The only real indigenous are black people living in Africa, every other group has moved into other places.
People of all colors and creeds have been warring and conquering and taking territories and resources throughout human history on every continent. Somehow people think that the Native American tribes were all peacefully coexisting and devoid of human greed. Not true at all. There's a reason some of the tribes fought with the European settlers against rival tribes they had been at war with for centuries.
Take the Black Hills for example. A narrow view of history states that "we" stole the land from the Lakota Sioux, true. But what's ignored is that the Lakota took it from the Cheyenne, Crow, Kiowa and Arapaho tribes who were living there and drove them out, violently.
And colonialism still exists today except it happens in the form of gentrification, eminent domain and corporate takeover. If someone defaults on their house and you buy it at a great price, should you feel guilty? I mean, you're participating in taking someone's home, their livelihood. You're displacing the original inhabitant.