Hiding behind that sort of arguement shows how pathetic the arguement really is. Fact remains, Native Nations owned this land every bit as much as we own property today because laws say we do. Difference was their law wasn't codified in some book and located at a capitol. And inventing laws out of thin air and using them to say we now own all this land and the natives don't because they don't have our kind of law is the worst kind of arguement. It's claiming our way of doing things is superior to everyone else's. Thus we can roll tanks in to Canada, plant our flag and say this is now our's because we say so. It's like if a child steals property from another child then insists it's their's becase they currently have possession of it. It no more makes any sense than settlers own the land their settlements were built on. Making that claim is to ignore the peoples who already lived there somewhere nearby and up until that moment had no need of fencing it off to denote property.
They owned nothing. For one thing, the Indians believed that land could not be owned by human beings. They had no concept of land ownership. All land belonged to the Great Spirit that let human beings use it. There was no nation, no borders, no indicia of land ownership.
If we were invaded by some foreign force that said they were going to take America, colonize it and plant their flag they can certainly do so and if they have the power they will be successful. It's something that happens to people that lose wars.