I think that repressing an awareness that we're living on stolen land is a common white habit. Where does that habit come from? Perhaps keeping that awareness more in mind, let alone doing something about it, would cause too much cognitive dissonance. Too much conflict between a conception of our lives as basically normal, benign and good, versus the reality of what many of our comforts have cost other people.
It's likely the case that most members of other non-Native groups in the U.S. also don't know which groups of people first occupied the land on which they live. Nevertheless, knowing that, and somehow taking responsibility for it, is a stronger ethical imperative for white people in the U.S. than it is for others. That's because the land was taken by white people, in the explicit name of white supremacy, and also because white people today still benefit the most from that theft.
In her book Revealing Whiteness: The Unconscious Habits of Racial Privilege, Shannon Sullivan explains the underpinnings of contemporary white justifications in the U.S. toward ownership, not only of formerly indigenous lands, but also of indigenous people themselves:
From white America's perspective, given that Native Americans did not know how to or lazily refused to work the land properly, it was appropriate that white Americans took it over. Such appropriation was not seen as theft, and not only because the United States sometimes paid for the land. More importantly, it was not theft because the lands were seen as vacant. Utilizing the environment by regularly moving from one place to another, Native American agricultural methods were not sedentary and were not recognized by Euro-Americans as signs of Indian occupancy of land.
With the rhetoric of vacuum domicilium, Euro-Americans declared these supposedly unoccupied, vacant lands as available for settlement. If Native Americans would not properly settle the land, nothing prevented white Americans from doing so. Morever, the Christian God, who was on the side of progress and civilization, required that Euro-Americans conquer the wilderness if Native Americans would not or could not do so.
Euro-American appropriation of land also was not seen as an instance of theft because there were no full persons from which to steal. Native Americans were merely subpersons because of their inappropriate relationship with the land. Even worse (from a Euro-American perspective), Native Americans' refusal to individuate themselves through land ownership meant that they were virtually indistinguishable from the land and the "wild" nature of which it was a part. In other words, white Americans recognized Native American kinship with the land only insofar as such recognition worked in favor of white America's interests in ownership.
On the one hand, white Americans often impatiently dismissed Native Americans' claims that the land was their kin and it should not be sold or farmed in Euro-American ways. As General Oliver Otis Howard responded to the Nez Perce chief Toohoolhoolzote while in negotiations with him, "Twenty times you repeat that the earth is your mother. . . . Let us hear it no more, but come to business at once." Native American kinship with the land was seen as irrelevant to the question of how and by whom the land would be used.
On the other hand, Native American kinship with the land was extremely relevant to this question because it revealed the (alleged) inadequacy of Indian ontology. Native Americans were not people but part of the wilderness that was not (yet) under the control of "man." Native American kinship with the land was cruelly used against Indian tribes, promoting rather than hindering U.S. appropriation of Indian territory.
As part of the land in need of appropriation, Native American people became pieces of property to be owned and exploited by those (white) individuals who could bring wilderness under control. They could be moved around at the pleasure of white America, which demanded more and more land as the British colony and then new republic grew. Social evolution, the growth of nationalism, and the development of American political institutions were all seen as dependent upon the western movement of the frontier between civilization and savagery.
Americans were seen as embodying "an expansive power which [was] inherent in them" and which produced their "universal disposition . . . to enlarge their dominion over inanimate nature" [Phillip Deloria]. Native Americans were merely one component of "inanimate" nature in need of such dominion. Forcibly moved westward and then restricted to discretely bounded reservations, Native Americans were the targets of a Euro-American geo-spatial agenda that both relied upon and reinforced a white ontology of ownership.
As the frontier began to close -- officially its end was declared in 1890, when all the territory occupied by the United States had at least two people per square mile -- white America began to romanticize nature, including the life of the "savages" who were part of it. Put in their proper place through the conquering of the wilderness, Native Americans now could be appreciated for their closeness with nature. The "primitive" setting of the uncivilized wilderness was seen as offering a needed antidote to the immorality, conflict, and materialism of the increasingly large urban centers of the United States. The wilderness of nature would help ensure that white Americans' refinement did not make them too soft. It also served as a cultural resource that proved the superiority of the United States to Europe, which was seen as artificial and inauthentic because overcivilized, and thus unnatural.
But the shift from a pioneer to a romantic attitude toward Native Americans did not lessen white America's appropriation of them. Native American were and generally still are considered as pieces of property owned by white America to do with what they please, only now this "knowledge" of Native Americans by white people is much more unconscious than conscious. White habits of ownership of Native Americans generally have not been eliminated; they have only changed the form of their expression. Rather than something wild to consciously set out to conquer, Native Americans -- espeically their religious traditions and rituals -- tend to be unconsciously appropriated as exotic objects for Euro-American use, pleasure, and consumption.
Because Sullivan's overview here focuses on what Euro-Americans have done and continue to do to Native Americans, it doesn't include a point that I think should be added -- it's not like Native Americans have taken all of this lying down.