Accompanying Elbegdorj's post were maps of the Mongol Empire of the 13th and 14th centuries. One shows the breadth of the vast but short-lived empire, which at its peak covered 9 million square miles.

At its peak, the empire spanned a massive 5.5 million ... until the 11th century. The Mongol empire rose in the 13th century when a group of central Asian nomadic tribes banded together under ...