Mongol Empire

The Mongol Empire under Genghis Khan stands as the largest contiguous land empire ever, spanning 24 million square kilometers—an area 57% larger than the Roman Empire's 5 million square kilometers and covering 16% of Earth's total land. Its Pax Mongolica unified Europe and Asia through trade along the Silk Road, yet its conquests resulted in 40 million deaths, eliminating roughly 10% of the world's population at the time—a human cost that exceeds the population loss of the British Empire's colonies combined. This dual legacy of connectivity and devastation shapes its historical rank.