I deliberately stayed away from the Injuns. I'll say this: there were so many different tribes that you'd have to take it case by case. In some cases, we butchered them -- or rather, some of your ancestors did, I was still mucking around in the mud in Slovakia for my Austro-Hungarian overlords. I'm sure we weren't above the occasional pogrom or gypsy murder, though, just to keep up with the Joneses. We were Not At All Nice to the Ruthenians, for instance.
In some cases, they were Terminator hunter-killers, and the rule there is kill or be killed. Those tribes were as rough on their neighbors as we were to them, and good riddance.
In most cases, we killed off their cultures by moving them around like game pieces, a treaty broken here, a nasty bit of crap Oklahoma scrub land there. Nobody was really thinking about the sanctity of aboriginal culture in the 19th century, though, so I'd chalk that up to "stuff we did then without a thought that today would be widely considered criminal." Like owning people. You know, our moral forfathers. Or rather, yours... see above.
The Indian Wars -- at least the early incarnations when there were real threats of raids on major white settlements -- remind me a lot of the GWOT. Fear, loathing, racism, indiscriminate killing, all in the name of high-sounding ideals and all bunk, on both sides. But at the same time, irritatingly, a major threat to both sides bordering on (as it turned out, for the losers) existential.
Given only two options, it's better to survive and write agonized apologies to the peoples you have killed off than to lose and be mourned. Hopefully, given some principles of law above ethnic and national interests that are now starting to penetrate mankind's eternally dense skull, those are no longer the only two options.