You might enjoy the book 1491 a lot - it goes over what populations existed before contact, and even explores the period when people would make decisions between whether they would stay a colonial resident or join a native country - and vice versa. Turns out it was very much down to the person.

Of course, it also has the mind-blowing fact that we lost roughly 92% of the population of the Americas to disease - which is how the Europeans walked into the "New World" so easily, but also why they had to start importing slaves from Africa. The author frames it as if we just suddenly lost all of China - and laments the cultural exchange we've lost as a result.

10/10 read, would recommend if you like the topic.

Probably using the same system that they evolved elsewhere. Humans be humans

Depending on how long they would be isolated.

Central american powers were starting to play with the Empire idea when europeans came along.

They might have had a Genghis Kang sooner or later.

Also contact by trade would have been almost as lethal as the conquest. Remember that most death were because the diseases the europeans brought with them.

there would be things like passenger pigeons that wouldnt go extinct, plus rare plants that became extinct due to development in a specific area where it only survived.

You call this evolution. It's humanity devolving. At least natives were free people.

Land Back.