Lot of callousness in that comment.

> Possibly

Definitely.

> at some point someone had to be the first humans in an area

Yes, and we know who they were. Hundreds of different tribes, spanning from coast to coast.

They came during the last Ice Age, crossing over the Bering Straight which was solid ground at that time.

The way American settlers treated the native peoples is not something that can just be "possibly"-d away.

"Possibly" in that comment refers to the possibility that the GGP comment was referring to the native peoples, rather than the meaning you took from it.

But how much of that land was actually "owned" by the people who actually first settled it? Didn't they have their own disputes and conquests?

Anyway the idea of land "ownership" is kind of stupid in the first place. You can't "own" land, you can just possess it under the rules of some kind of system of power.

100,000 years ago for most of the Old World, 40,000 years ago for Australia, and 6000 years ago at the maximum for Southern America's (12kya for North America).