So, Guns, Germs, and Steel was a book from 1997 that tried to explain why Europe (and to a somewhat lesser extent Northern Africa, and Asia) went around conquering everydamnedplace, and sub-Saharan Africa and the Americas didn’t.
The basic theory goes about like this:
Europe and Asia had a lot of easy-to-domesticate plants and animals, while Africa and the Americas basically didn’t. Part of this was just chance (wheat, for example, practically self-domesticated, while you probably wouldn’t even recognize the wild ancestor of corn as being related to modern corn), and part of it was geography (basically, Eurasia was mostly east-west, so anything that was domesticated could spread a good way without having to adapt to a new latitude, but sub-Saharan Africa and the Americas are more north-south oriented, so any local domestication event was a lot harder to spread around.
In particular, Europe and Asia had large domesticatable animals that they could use to do work, like pulling plows. This was a major force multiplier for farming.
So, Europe and Asia developed large population bases, with fairly intensive agriculture, leading to enough surplus food that a good fraction of the population could do things besides grow food. This lead to technology advances, nation states, and so on, and thus to the ability to go around and technologically dominate everyone else.
And the fact that these large populations had a lot of animals led to zoonotic-origin plagues, like bubonic plague and measles, which spread through cities. These, in turn, essentially wiped out the natives of the Americas (who hadn’t had generations of selection weeding out anyone who was too susceptible to them), making the conquest there… especially easy for European-origin people.
So, that explains why Europe basically became the boss of the world, at least for a while. But the next question, not really addressed in the book, is… why did Europe and Asia have so many large animals they could domesticate, while Africa and the Americas didn’t?
I have a further hypothesis to explain that one, and it has to do with hunting.
Most of the traits that make an animal easy to domesticate also make it easy to hunt. And humans tended not to domesticate animals until they got to a level of population density and/or sophistication that hunting, alone, was not quite enough.
Humans were, initially, not great hunters, or at least nowhere near as good as we were eventually going to get. So, the animals around us, back in Africa, evolved with early proto-humans hunting them as an evolutionary pressure, but we weren’t good enough at it to cause anything even close to extinction. So, by the time we got to a level of sophistication where we would have considered domesticating animals, there were lots of large animals, all with lots of adaptations to make it hard for us to hunt (or domesticate) them.
By the time we got to Europe and Asia, we were decent at hunting, but not really “wipe out entire species” good. So we reached “Welp, better domesticate things” population densities while things like cows, goats, and horses were still around.
But by the time we got to the Americas? We were getting good at this s***. Between us and some climate shifts (that helped things along), the potential domesticates (and many of the other large animals, especially any that were easy to hunt) were wiped out well before we got to “You know, maybe we should do something besides just run after dinner with a pointy stick” population densities.
Science is Really Weird 