What Was the Largest Contiguous Empire in History?

Mongol Empire

Explanation:

The Mongol Empire was the largest contiguous empire the world has ever seen. The Mongol Empire covered 9.15 million square miles of land - more than 16% of the earth's landmass. The empire had 110 million people between 1270 and 1309 — more than 25% of the world's population

Historic sources present disparate accounts of Ivan's complex personality: he was described as intelligent and devout, yet given to rages and prone to episodic outbreaks of mental instability that increased with his age, affecting his reign. In one such outburst, he killed his groomed and chosen heir Ivan Ivanovich. This left the Tsardom to be passed to Ivan's younger son, the weak and intellectually disabled Feodor Ivanovich.