I just... Ow! Up until now on Crash Course, we've been focused on city-dwelling, civilizational types. But with the growth of the Silk Road, the nomadic peoples of Central Asia suddenly become much more important to world history. Most of Central Asia isn't great for agriculture, but it's difficult to conquer unless you are, wait for it, the Mongols. It also lends itself fairly well to herding, and since nomads are definitionally good at moving around, they're also good at moving stuff from point A to point B, which makes them good traders. Plus, all their travel made them more resistant to diseases. One group of such nomads, the Yuezhi, were humiliated in battle in the 2nd century BCE by their bitter rivals the Xiongnu, who turned the Yuezhi's king's skull into a drinking cup, in fact.