The Cost of War

This is taken from Steven Pinker's new book.  He provides some interesting comparisons.

*Deaths were calculated against global population at time, then scaled up to mid-20th century level

*Median/mode of figures cited in encyclopaedias or histories. Includes battlefield and civilian deaths

Conflict	Century	Death toll*	Death toll (20C equivalent)	Rank ▴
An Lushan revolt	8th	36m	429m	1
Mongol conquest	13th	40m	278m	2
Middle East slave trade	7th-19th	18m	132m	3
Fall of the Ming dynasty	17th	25m	112m	4
Fall of Rome	3rd-5th	8m	105m	5
Timur Lenk	14th-15th	17m	100m	6
Annihilation of the American Indians	15th-19th	20m	92m	7
Atlantic slave trade	15th-19th	18m	83m	8
Second world war	20th	55 million	55M	9
Taiping rebellion	19th	20m	40M	10
Mao Zedong (mostly government-caused famine)	20th	40M	40M	11
British India (mostly preventable famine)	19th	17m	35m	12
Thirty years' war	17th	7m	32m	13
Russia's “time of troubles”	16th-17th	5m	23m	14
Josef Stalin	20th	20m	20m	15
First world war	20th	15m	15m	16
French wars of religion	16th	3m	14m	17
Congo Free State	19th-20th	8m	12m	18
Napoleonic wars	19th	4m	11m	19
Russian civil war	20th	9m	9m	20
Chinese civil war	20th	3m	3m	21

Source  Steven Pinker, Better Angels of our Nature: Why Violence Has Declined (2011).  Amazon.