IIRC (I have a copy of 1491 here, just too lazy to flip through it), South America was the last continent to be settled by humans. They were literally just arriving there at the same time that the Fertile Crescent was getting their Neolithic Revolution on. By the time they developed agriculture, it had already been in place for millennia in the Old World.
The first South American culture took root around 1000 BC, compared to say Sumeria or Old Kingdom Egypt ca 3000 BC. The Maya had cities with pyramids a couple hundred years after that, the Aztecs and Inca completed wars of conquest to unify their region ca 1000 AD (the Inca had literally just finished theirs in 1450 IIRC), compared to say the Assyrians wrecking the Near East in 2000 BC. The South American civilizations had cities, they had writing, they had centralized economies... the general impression I get is that they were about equivalent to a Bronze Age level of sophistication. So they were developing at a roughly similar pace to the Old World, they just started a couple thousand years behind. I don't see how you can close that big of a gap without an ASB point of departure.
That Bronze Age part got me thinking - none of the American cultures developed bronze. It would be the epitome of arrogance to assume that the Eurasian track of development is the only one possible and that you have to go from copper -> bronze -> iron in a linear fashion, so I'm not saying that. It's similar to how those societies never needed wheels. But as the American civilizations continued to advance, it would be interesting to see what alternative technological paths they would take.
Not true. Humans were present in South America at least by the times of the Clovis Culture (14.000 years ago). First urban civilizations in Peru date to 3100 BCE.
en.wikipedia.org
Andean civilizations were very advanced by the time, with complex cities and irrigation canals comparable to anything found in Sumeria or Egypt. However, Norte Chico at least lacked pottery (a very interesting difference! subsequent cultures did have very complex pottery traditions) and metallurgy. Metallurgy was
very well developed in the Andes by the time of the Incas and earlier, but for one reason or another, it was mostly reserved for religious items and social status. It might be just a reason of practicality: stone and textiles were very abundant and useful tools, so they wouldn't necessarily see the use for metal tools. However, applied metallurgy opens the door to many possibilities, and could
Many people will inevitably mention domestic animals as a prerequisite for *advanced* civilizations. I don't see them as very relevant. Horses, cattle and pigs do not do well in the Andes. The Andeans domesticated the animals most useful in their enviroment: llamas and alpacas. Llamas cannot be used as calvary or transport huge loads, but they're prefectly adapted to the Andean enviroment, can climb mountains and transverse deserts, and give the ever useful textiles and meat (though they apparently aren't very useful for milk). While a better source of protein would be nice (apparently the Andeans domesticated some birds and other small animals for food besides guinea pigs), llamas fit perfectly.
However, the most important factor here is the enviromental (and thus political one). The major gap between the Norte Chico Civilization and the Chavín city states was because (AFAWK, this is a all-new area of discovery) the cities of the Norte Chico civilization collapsed due to drought and mismanagment of natural resources. Unlike Egypt or Mesopotamia, the Andes don't have a major permanent river, and so drought is a recurring scourge, that makes empires and cities collapse after a brief period of prosperity. Chavin, Huari, Tiwanaku, all seem to have collapsed because of struggles caused by drought. And so there was little, time, so to speak, to unify the Andes in a coherent whole, though they had shared characteristics in religion and culture. The Incas managed it, and it seems that the technology of terrace farming and better social organization might have been a better guarantee against droughts. Though we'll of course never know.
I don't know enough about Mesoamerica to comment in there, but I'll just note that they had no domestic animals or metallurgy of note, and no American culture used the wheel as anything but a toy, yet they were able to create and maintain great cities and long-ranged trade routes.
If the American cultures had developed applied metallurgy earlier, maintained better trade routes (probably by sea, though there is evidence that those trade routes did exist in a limited way) to allow better spread of technology and ideas, and maybe had better political organization (a topic that we know little about because lack of written records; we know barely anything of pre-Incan society and politics), yes, absolutely, they could have an iron-age *techlevel* by 1492.
As for the Old World... the thing is, once technology is learnt, it's difficult to unlearn it. The Dark Ages were a period of decline in western civilization but people still knew how to smelt metal and build cities. And even if there's a massive collapse in one area of Eurasia, others might remain unaffected. The only way I see is for urban civilizations to be destroyed by nomads early on and repeatdly, or plagues with eeath levels of those that devastated the Americas.