What would have happened if the American continents had no contact with Europe? This could be for any reason (Columbus never makes it back, the Mongols manage to raze everything from Istanbul to Lisbon, etc.), just so long as there is no long-term contact with non-Americans.
As far as I can tell, history follows certain patterns, and pre-Columbian mesoamerica fits those patterns perfectly. In fact, Mesoamerica is a lot like Mesopotamia is for Eurasia, with the Inca corresponding roughly with the Egyptians. My belief is that the Aztecs, like the Toltecs and Olmecs, all function as the ancient Mesopotamian powers, like Babylon, Assyria, and Persia, do to the east; as the base of local civilization. Eventually, after the Mesoamericans tire themselves out, a foreign group (the Apache?) establish a similar culture, but more advanced - much like Greece. And, eventually, another power further away from them (Louisiana? Florida?) takes over massive territories and establishes itself as the base of American culture: essentially, that will be Rome.
What do you guys think?