It is generally estimated that the conquests of Genghis Khan and his immediate successors were responsible for the deaths of approximately 40 million people.
This figure is staggering: at the time (13th century), it represented nearly 10% to 11% of the world’s population. To give a sense of scale, this would be equivalent to more than 800 million deaths if such a conflict were to occur today.
The Strategy of « Total Terror »
Genghis Khan did not use violence solely out of cruelty, but as a psychological tool of war.
When a city refused to surrender, the Mongol army systematically massacred almost the entire population after the victory (leaving only useful artisans and engineers alive).
The goal was to create such terror that subsequent cities preferred to open their gates without a fight as soon as they saw the Mongol banner on the horizon.
The Destruction of Vital Infrastructure
A large proportion of the deaths did not occur on the battlefield, but rather as indirect consequences of the invasions:
In Persia (modern-day Iran) and Central Asia, the Mongols destroyed the qanats (underground canals).
This transformed fertile areas into deserts, causing widespread famines that lasted for decades after the army’s passage.
The forced displacement of millions of people disrupted harvests and food supply chains.
The Deadliest Campaigns
In China, it is estimated that the population plummeted by tens of millions during the Mongol conquests (although epidemics and famines contributed as much as the swords).
In the Khwarezmian Empire (Persia), cities like Merv and Nishapur, which had hundreds of thousands of inhabitants, were virtually wiped off the map.
An Unexpected Ecological Impact
Surprisingly for historians and climatologists, this sudden population decline led to the abandonment of millions of hectares of cultivated land.
The forest reclaimed this land, resulting in a massive absorption of CO₂ (approximately 700 million tons). This is probably the only time in history when human activity caused a temporary global cooling of the planet.