Mesopotamia gave us writing, specifically a form of writing called cuneiform, which was initially created not to, like, woo lovers or whatever, but to record transactions, like how many bushels of wheat were exchanged for how many goats. I'm not kidding, by the way, a lot of cuneiform is about wheat and goats. I don't think you can overestimate the importance of writing, but let's just make three points here. First, writing and reading are things that not everyone can do, so they create a class distinction, one that in fact survives to this day. Foraging social orders were relatively egalitarian, but the Mesopotamians had slaves and they played this metaphorically resonant sport that was like polo, except instead of riding on horses, you rode on other people. And written language played an important role in widening the gap between classes. Two, once writing enters the picture, you have actual history instead of just a lot of guesswork and archaeology.