I was wondering to myself what would have happened (yes another what if thread) if the America's had not been conquered by the Europeans. Let's say for instance that the American Indians had developed their societies to this very day. I personally think that the Inca's and the Aztec would have eventually down the line would have gotten into a war with each other for hegemony for Central America, and the Main of the South American continent. I don't see North American natives going very much further then they already were.
The Aztecs would have expanded northwards into the Southern US, and all the way to Florida. Meanwhile the Inca would have in my estimation expanded further north as well into Venezuela and the Amazon rainforests. The Southern Crone region would still have un-sophisticated societies. Technologically one can only wonder what these people would have done. I wonder what you think especially in terms of probable technologies they would have innovated.
Another scenario is the Chinese settlement of America. The Chinese went to America before the Europeans, and they would have most likely created trade routes with the Americas, if the introverted and isolationalist Ming Dynasty stopped their worldwide expeditions. The interaction btwn the Chinese and the Inca, and Aztec obviously would have been much more peaceful then the Europeans, because the Chinese were not to colonize but to merely trade. Could such a long term Inter-continental trade btwn these two great civilizations saved the Americans, who knows the Chinese could have given them technology that was way ahead of European technology at the time, advanced guns, advanced ship design. But sadly the only thing that the Chinese couldn't give the Americans was their immunity to diseases which was the Americans greatest fault, and not of their own volition.

So what could have been? A great advanced civilization or one that would lag behind her conquers?

I personally think that the Inca's and the Aztec would have eventually down the line would have gotten into a war with each other for hegemony for Central America, and the Main of the South American continent

Machu Piccu is a helluva long way from Mexico City. Seems like it would be hard to move an army that far without the wheel, no? ;)

I'm not familiar at all with South American history, but didn't the Maya come in there somewhere? You just seem to mention Aztecs and Incas..

The Maya were goners before the Spanish even came to America, but we still are not sure as to why. The Inca empire spread from Chile to Ecuador in the North, and in my estimation was only to go expand further north, they had a well trained army, and efficent transportation network. The Aztec well they resided in Central Mexico, and I am not sure if they would have went North or South, in the South they already had Maya infrastructure, and they would have more resources. Eventually the two imo would met up, and well history would decide whether or not they would fight.