Well for one if the Mayans were still around, Americans wouldn't have gone crazy and bought guns and food to prep for the end of the world in Dec 2012, as they would have UPDATED their calendar hahaha.

There probably would have been some sort of war from the north against the French, British, or Spanish. The result would be fairly similar for the Southern Americans at least. A massive conflict could reshape the end result in the Americas depending on how successful the campaign was and who was involved.

Part of me thinks the Aztecs would have kicked the early United State's ass. If they had the chance to have limited interactions with Europeans, giving them just enough exposure to become immune to European diseases by the 1800, the Aztex empire would be all ove Washington's ass with superior numbers and home-turf advantage. That's implying that the U.S. would even go as far down as Mexico back then. 

Nah, the U.s would do exactly what they did to native americans. They had the tech and the drive to spread. If Mexico wasn't settled by europeans, then no doubt they would have.

Sad story of the world.

USA would have conquered all, we would have southerns instead of westerns and not a single south american country would have won the football World Cup.

They would be nearly extinct and the land would be completely devastated, with barely any technological, cultural and ethical advancement.

Hard to say. You see, throughout the course of history Europe, India and China concentrated over two thirds of the world's population. The first to go through medical advances and an industrial revolutions would face a demographic explosion with no precedents and would have to vent it somewhere. So I guess North America would be incredibly populous, probably over twice as much. Also depending on how things went, Siberia and Central Asia would have been effectively colonized instead of merely conquered by an empire as it happened here.

Mmm... so many implications. I might write an alternate history timeline about this.

That being said, South and Central America would probably end up like Africa today, perhaps a little better. That depends on how fast their populations would grow after the threat of tribalism and diseases were removed.

One of the biggest genocide in human history. If the Spanish/Portuguese never came, South America would've been much more richer and stronger.

They would be exterminated by the english instead like the american and canadians ones