The Mongol empire was the largest contiguous land empire in history. In 1279, at the height of the empire, the territory spanned from the Pacific Ocean to Central Europe.
Genghis Khan lead the Mongol army to slaughter millions of people and destroy entire cities, conquering more land in 25 years than the Romans conquered in 400. With such a powerful empire, how did Genghis Khan and the Mongol Empire eventually fall?
History.com: Genghis Khan
All Empires: The Mongol Empire