system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: why are the majority of wealthy/developed countries concentrated into the northern hemisphere of the world?

It seems that the northern half of the world contains most to all of the developed countries in the world. Why is this? My best guess is that explorers from Europe never settled too far south of the equator.
gpt
There's a really great book about this called Guns, Germs, and Steel that explains why some societies have gotten so much more progress than others.

A couple of things.

The "northern half" includes North America, which is one of the least advanced, historically. So saying that "the northern half" contains the most developed countries in the world is only partially true. If you take the United States, well, that's essentially a really large European colony, and can take advantage of Eurasia's natural advantage.

So that leads to the question: Why did Eurasia have that kind of advantage, anyways? Why did Europe colonize the world instead of Africa or South America? It's a couple of things, actually: The east-west axis of Eurasia, the availability of domesticable animals, and the availability of good quality metal ores.

The Americas are primarily north-south in their orientation, and it's obvious that there are larger differences in latitude than longitude. You can bring that awesome wheat variety you've just domesticated eastward or westward, like what happened in Europe, but it's hard to move that wheat north or south, where it's colder or warmer, and where the weather is probably different.

Secondly, Europe and the Middle East have by far the most large animals available for domestication, and that's a huge deal. When you have a large animal working your fields, you are a lot more productive, and the more productive you are, the more people your land can sustain. Agricultural societies are always a lot more dense than non-agricultural societies, and more dense societies can sustain more non-productive citizens like philosophers, artists, kings, and soldiers. 

Domestic animals also increase your ability to travel, and the amount of luggage you can tow around. When you're limited to smallish loads carryable in a hand cart, you're not going to be able to realistically trade as much as you could if you had a horse-drawn cart, and you're not going to want to go as far. You're not going to be able to really use the massive power of the wheel, because you can't scale up as far as you can if you had an ox-sized being hauling stuff.

Lastly, the advantage of iron and bronze over stone and wood is self-evident. If you have bronze, you're going to beat your stone-equipped enemies and can access iron. If you can access iron, you're going to defeat your bronze-equipped enemies and can access steel, and so on.

Surely I've missed something, but I've gotta go. Hopefully this helped!