2. The Three Kingdoms, during which period China existed in a state of continuous warfare, saw an estimated 40,000,000 lose their lives
The Three Kingdoms was a period of division within mainland China between the competing states of Wei, Shu, and Wu, lasting from 184 to 280. Beginning with the deterioration and eventual collapse of the Han dynasty, and concluding with the ascendance of the Jin, each rival faction claimed dominion over the others as the sole legitimate emperor. Eventually, after decades of war, in 263 the Shu was conquered by the Wei. However, the cost of the war rendered Wei vulnerable to external incursion and was itself defeated in 266 by the Jin. Unable to stand alone against the combined might of the enlarged Jin, Wu was conquered by the Jin in 280 ending the conflict.
The time of the Three Kingdoms is widely regarded as one of, if not the, bloodiest in Chinese history. A census taken in 280 following the reunification of the region under the Jin accounts for 2,459,840 households, encompassing 16,163,863 total subjects. This seemingly large figure was merely a shadow of the population during the preceding Han dynasty, under which 10,677,960 households included at least 56,486,856 individuals – a decline of more than 40,000,000 over the hundred year conflict.