The Mongol Empire (Mongolian: Монголын Эзэнт Гүрэн, Mongolyn Ezent Güren; 1206–1405) was the largest contiguous land empire in history, covering over 33 million km² (12 million square miles) at its zenith, with an estimated population of over 100 million people. It was also the second largest empire in history, after the British Empire. The Mongol Empire was founded by Genghis Khan in 1206, and at its height, it encompassed the majority of the territories from East Asia to Eastern Europe.
Mongol Empire included large parts of Asia and parts of Europe as far west as Moscow and Kiev. Mongols killed millions and subjugated hundreds of millions even though their army probably never exceeded 250,000. Part of their success was due to alliances made with Turkic and other Asian nomads.
It started out as a Mongol Nation of unified Central Asian confederations such as Mongols, Naimans, Uighurs, Merkits under Genghis Khan, but got territorially expanded after numerous outward conquests such as against China, Middle East and European regions under multiple Khans and Khagans. After unifying the Mongol and Turkic tribes, the Empire expanded through numerous conquests throughout continental Eurasia starting with the conquests of the Western Xia in north China and the Khwarezmid Empire in Iran.
During its existence, the Pax Mongolica facilitated cultural exchange and trade between the East, West, and the Middle East in the period of the 13th and 14th centuries. The Mongol Empire established commercial and political connections between the Eastern and Western areas of the world. It is probable that the Mongols and merchant caravans inadvertently brought the plague from central Asia to the Middle East and Europe. The Black Death swept through Eurasia, killing approximately one third to one half of the population (according to some estimates) and changing the course of Asian and European history.
The Mongol Empire was ruled by the Khagan. After the death of Möngke Khan, it split into four parts (the Yuan Dynasty, Ilkhanate, Chagatai Khanate and Golden Horde), each of which was ruled by its own Khan.