The Mongol leader who unified the nomadic tribes of the steppe and conquered the largest contiguous land empire in history — bringing catastrophic destruction to settled civilizations while creating the Pax Mongolica that opened Eurasia to trade, ideas, and plague on an unprecedented scale.
Genghis Khan killed so many people — perhaps 40 million — that forests grew back over abandoned farmland and global temperatures briefly fell. He also created the largest free-trade zone in history and connected China to Europe for the first time. The scale of both the destruction and the creation is without historical parallel.