This trading eventually led Mesopotamia to develop the world's first territorial kingdom, which will become very important and will eventually culminate in some extraordinarily inbred Habsburgs. The city-state period in Mesopotamia ended around 2000 BCE, probably because drought and a shift in the course of rivers led to pastoral nomads coming in and conquering the environmentally weakened cities, and then the nomads settled into cities of their own as nomads almost always will, unless, wait for it, you are the Mongols. These new Mesopotamian city-states were similar to their predecessors in that they had temples and writing and their own self-glorifying stories, but they were different in some important ways. First, that early proto-socialism was replaced by something that looked a lot like private enterprise, where people could produce as much as they would like as long as they gave a cut, also known as taxes, to the government. We talk a lot of smack about taxes, but it turns out they're pretty important to creating stable social orders. Things were also different politically, because the dudes who'd been the tribal chiefs became like full-blown kings who tried to extend their power outside of cities and also tried to pass on their power to their sons. The most famous of these early monarchs is Hammurabi, or as I remember him from my high school history class, the Hammer of Abbe.