The Mongol Empire was an empire from the 13th and 14th century spanning from Eastern Europe across Asia. It is the largest contiguous empire in the history of the world. It emerged from the unification of Mongol and Turkic tribes in modern day Mongolia, and grew through invasions, after Genghis Khan had been proclaimed ruler of all Mongols in 1206. At its greatest extent it stretched from the Danube to the Sea of Japan and from the Arctic to Camboja, covering over 33,000,000 km2 (12,741,000 sq mi), 22% of the Earth's total land area, and held sway over a population of over 100 million people. It is often identified as the "Mongol World Empire" because it spanned much of Eurasia. As a result of the empire's conquests and political and economic impact on most of the Old World, its wars with other great powers in Africa, Asia and Europe are also believed to be an ancient world war.