They were not, at that time, remotely interested in humane values. No international power in its empire-building phase, recognizes the sovereignty or autonomy of nations with less fire-power than their own. They come to enlightened philosophies regarding human liberty, dignity and rights only in decline. And then, just the literati: you still have to beat every inch and ounce of social justice out of their governments at home.
If the immigrant is the petitioner, asking to be allowed into the host country's culture. Not if the decision to assimilate a sub-group - say the the Uyghurs in China - it doesn't work at all; they always resort to genocide, fast or slow, overt or covert.
They weren't migrating; they were colonizing. That is an inherently aggressive act : a strong invading force taking over a weak indigenous population. Immigration is a contract between an individual and a nation-state, where that individual's only protection is the degree to which the nation-state adheres to its promise.
Record? Not of an official pogrom - just a few local incidents and a few unprovoked attacks by army units - though some recent historians have been a little forthcoming about the nature of some murky past events. It was not usually overt and fast, but a whole lot of native people were killed one way or another, and there certainly was a concerted, protracted official policy of suppressing native culture and language, of disrupting communities and their livelihood. More overtly, there was forcible seizure, of natives' land and hunting/fishing grounds by government agencies - along with the unacknowledged incursion of settlers (forest-burning, wildlife-eradicating, fence-building settlers) and private mining operations on what were officially designated as native territories. And, of course, some pretty harsh law-enforcement (which is still going on, btw) and the famine
https://uofrpress.ca/Books/C/Clearing-the-Plains
which was not directly caused by the Canadian government - all the settlers, though most actively the American ones, had a gun in killing off the bison - but the administration and the railroad barons certainly took full advantage of the resulting hunger.
I'm also aware that many settler communities lived peaceably alongside, and interacted amicably with native communities. It wasn't a full-out national campaign of eradication, so maybe genocide is a degree too strong. But 'assimilation' suggests a desire, or at least willingness to include "the other people" among one's own, and I see no indication that any such desire or willingness existed - ever.
