Also, no interrupting the Thought Bubble. After uniting the Mongols, Genghis Khan went on to conquer a lot of territory. By the time he died in his sleep in 1227, his empire stretched from the Mongol homeland in Mongolia all the way to the Caspian Sea. Thanks, Thought Bubble. So that's a pretty good looking empire, and sure, a lot of it was pasture or mountains or desert, but the Mongols did conquer a lot of people too. And in some ways, with Genghis's death, the empire was just getting started. His son, Ogedai Khan, expanded the empire even more.