Which historical conflict killed the most people?

The story behind the answer

World War II caused an estimated 70–85 million deaths (about 3% of the world’s population), far surpassing the others. Its unprecedented scale—global theaters in Europe, Asia, Africa, and the Pacific—combined with industrialized warfare, genocides (including the Holocaust), strategic bombings, starvation, and disease led to massive civilian as well as military losses.

For comparison, estimates for the Mongol conquests are roughly 30–40 million, the Taiping Rebellion about 20–30 million, and the Three Kingdoms War perhaps 20–40 million—large but still below WWII. A memory tip: “World War II = the world’s worst in lives lost.” The war’s devastation reshaped the international order, spurring the creation of the United Nations and a global push to prevent conflicts of similar scale.