The Post-Classical Period features two groups that come from (historically speaking) nowhere. The first we've already covered: The Arabs. The next: The Mongols. Get ready for earth's biggest Empire. John Green's "Exception" to every rule, the Mongols are one of the most interesting phenomenons in all of History. Think a nomadic group in the 13th century could never rise up under the rule of one man and conquer most of the known world? Think again. It happened. Enjoy the Mongols...