@goatprairie : I know one thing for sure: the tribes would have eventually faced the same sweeping plagues that killed them off, largely before our ancestors settled the cleared-out continent.
There has also been a movement by leftist historians to claim that there were many more millions of Indians inhabiting the area north of the Rio Grande than there actually were.
Some claim the number of 15-20 million inhabitants. They made that assumption based on a few burial spots they found and made some funny calculations.
There were probably only about 2-3 million Indians north of the Rio Grande at the time European settlements started. If it had been a higher amount, there would be better evidence than what the leftist historians claim.
There were no large populations in one area (cities) an indicator of high numbers of humans.
That means most of the country was empty (like much of the west is now), and there was plenty of room for new people.
I doubt any of the leftist historians are planning to make a permanent return to Europe to make things right. Like all leftists they just like to bitch and moan about Evil Whitey. Evil Whitey for whom the Indian tribes would still be living in primitive conditions.