In South America there were great technological and intellectual advancements. The Mayans and Incans were great astronomers and mathematicians. But I take your point. They were technologically well behind other civilizations. Mostly, though, what you're talking about has to do with the use of Metals. Evolution, both biologically and culturally, have a great deal to do with chance. You might also ask the question about why humans developed our superior intelligence while our ape cousins did not. The questions are very complicated. It's all about what advancement would benefit a given species at a given time. Europeans were far more sedentary, utilizing agriculture to a greater degree. Because their lives were more stationary and they didn't have to keep moving, they had more time to develop a more complex society, with greater specialization of labor. You see a metal and think, hey, what can I do with that?

Native Americans in North America were more nomadic, moving constantly from place to place in search of food. If you move a lot, it's harder to develop complicated technologies because you have to continually lug all of your possessions around with you. Or maybe its something that no one's thought of yet. The point is that there are many methods of survival, which is what evolution is really all about. There is no right way or wrong way or inevitable conclusion that all people are destined to reach. If, for some reason, intellect suddenly became and evolutionary burden, then you would see a drop in intellect, it's that simple.

And chimps didn't become smarter because they apparently didn't need to. They survived just fine with their more limited intellect.

It's all chance and circumstance…

This is an extremely complex subject — not one easily answered in a few sentences. There is an excellent book "Guns, Germs and Steel" by anthropologist Jared Diamond that goes into all of the details. Among them: Humans have only occupied the Americas for around 16,000 years, less a quarter of the time that modern humans have been in Europe, Africa and Asia. They had a much less dense population, they had few native animals that could be domesticated like the horses, cattle, swine of the Old World. Another difference was that the North and South American continents were oriented north to south instead of east to west like Europe and Asia. The problem with that is that if you develop a type of agriculture, it will work in the same climate zone so such innovations tend to spread east and west, they don't work in areas to much farther south or north. It was simply easier for the larger and longer established civilizations, with greater population density and common climate zones, to share and spread technology. The distances, geographic barriers and lack of crowding lead to far less population concentration and innovation sharing in the New World.

You left out beasts of burden. The new world didn't have any. Alexander and Genghis had horses and you know how well they did.

Humans reached the Middle East and Europe perhaps as early as 200,000 years ago. Man likely reached the Americas 20,000 years ago or less.

Swords were in use. In fact they were sharper then any steel the Europeans could make. Why would swords make that much of a difference? Many of the ancient battles in the old world were won by spears as bronze and copper bent and were soft.

What the Europeans had on their side was disease. Cortez got beaten the first time he tried to conquer the Aztecs. He won only after a epidemic of smallpox ran it's course. In many cases settles moved into lands where the population had been decimated by imported disease.The Nose had steel swords and gave up trying to establish colonies in the Americas