I think the Slavs are the more apt comparison to indigenous Americans—the drive for Lebensraum meant the frontier would be pushed out and their territory would be claimed. The people were (not would be, because they started implementing this plan) exterminated in large part, kept as servants (labor) to the Aryans—and in fact Slavs (especially Poles of corridor) with features judged to be Nordic were to be culturally Germanized and integrated to expand the Volk. The extermination of the Jews was never about territory or a side effect of Nazi ambitions, it was the Nazi ambition. There is a lot written on this bit.

America like England was seen as essentially a civilization produced and supported by Aryans even if other “races” were there. So it always fit in the plan as part of the sort of Aryan empire.

Japan was allied, obviously, and there was some theorizing about their racial superiority over other Asians, but they were obviously not Aryans (maybe not so obvious, since Indians and Iranians were somehow)—the alliance was clearly political, and the assumption was that Japanese would rule Asia and Germany stayed out of all that, but who knows what thousand-year plans Hitler had for Asia (at least I don’t).

Ultimately the Third Reich imagined itself as an empire (that’s what Reich means, chiefly), not just a pure Aryan nation and folk community with expanded territory. That meant subject nations. But they didn’t want to become a pluralistic empire like all the others, they wanted themselves to maintain “purity”—and yet to rule the world.