As you know, I'm a big fan of creating worlds and then colonizing them. Some of the research I do towards this end is interesting enough that it can stand on its own. Like this post about the very early years, when hunter-gatherers gave way to sedentary farmers.
If you have any familiarity with the subject, you might have the impression that this was an explosion or revolution. Poom! Now we're all farmers and we have cities, high population density, specialization, and so on.
That's not really true. Farming flickered on and off for thousands of years before it really took root, and even then its spread was pretty rough. I don't think there's any textbook-endorsed reason for this "flickering", but a little thought yields an obvious answer.
The stuff we grow on farms today is not wild stuff, it's tame stuff. It's domesticated, just like the dog: we brought in wild barley and bred it decade after decade until it behaved like we wanted it to.
So the first farmers were starting with wild plants. Wild plants that grow perfectly fine wherever they currently grow in the wild, and don't really grow much better if carefully tended. It's easier just to go pick raspberries than grow bushes of them. Sure, you might plant some raspberries along the river bank so that when you swing by again in a few years you'll have plenty of raspberries, but you aren't going to sit down and watch.
In order to successfully go agricultural, your farm needs to produce an immense yield compared to the wild land's yield. Factors that can improve your relative yield are: plant domestication, irrigation, and having crappy wild yield (or being unable to range very far to collect it). I imagine that early farmers would often need all three of these factors in order to really consider agriculture as a way of life.
You may think that plant domestication is kind of one-way - once someone domesticates it, it stays domesticated. However, that's probably not really true. Unfortunately, even a successful farmstead is in a tremendous amount of danger. Not just from raiders or weather, but also from soil degradation and salinity buildup. Every year, your field probably produces less than it did the year before. The farm goes bust, the slightly-tamed crops interbreed with their wild brothers.
Eventually, there were enough pseudo-domesticated strains of cereal grass running around that farming could finish the job and properly take root. This seems to have happened on earth about 10,000 years ago, although there are signs that it took root and then un-rooted many times before.
The Fertile Crescent is the famous "birth of agriculture" spot, and this is because the crescent has long dry seasons and short rainy seasons. Grasses grow in these locations instead of dense forests, and that has two effects. 1) long grasses produce excellent farming soil, and 2) cereal grasses are pretty adaptable, and can be domesticated to higher yields very easily. The highly variable terrain also makes settling down a bit more attractive: it's harder to range very far on foot.
These three conditions happen to satisfy two of the three preconditions mentioned, and irrigation was also possible, so the crescent was an ideal place for agriculture to set in.
In Africa, things like millet and coffee were being domesticated, although not at quite such an early date. The places these agricultural revolutions took place in (such as the Ethiopian highlands) have many of the same characteristics as the Fertile Crescent: wet season and dry season, variable terrain, available water.
Asia and America followed in the same kind of pattern.
Why does this matter?
Well, if you're putting down initial settlements in a world-building game, and you're starting at the agricultural revolution, then this tells you precisely where to put them: on variable terrain with a wet and dry season.
Moreover, it also gives you a new lever. Normally, farms are treated as farms. However, farm technology is not simply irrigation and crop rotation. The crops themselves are a technology. The products we grow today have spent thousands of years slowly shifting from the original versions. Over time and as long as war and ruin don't interfere, that technology will improve.
If you really want the game to rely on food, you can also work in soil degradation and salinity. The middle east wasn't always a desert: many of those lands were lush and fertile until they were catastrophically overfarmed. There's quite a bit of evidence that many of the mostly-forgotten great old empires from across the world collapsed due to overfarming.
Anyhow, I actually wanted to post on weather simulation. Maybe some other day.