At this rate, it would take you only one hour to decide that this is a really depressing job, and you would have been better off working as a checkout clerk at the Food Lion instead. By my calculation, there have been 165 wars or tyrannies of the 20th Century which have killed more than 6,000 people. Five of these events claimed more than 6 million victims. Twenty-one events claimed between 600,000 and 6 million lives. Of course, all these numbers are subject to a wide margin of error and a rancorous debate.
Wars are messy, and tens of thousands of people can easily disappear without a trace.
The worst atrocities take place in the dark, unseen and unrecorded. Estimated death tolls can therefore vary wildly, spanning several orders of magnitude at once. It's not at all unusual to have an upper estimate be two, maybe three, times the lower estimate. To arrive at the numbers illustrated on the maps, however, I have tried to be extremely mainstream. I tried to find the most commonly quoted body count, and then I rounded the number to the nearest triangular number.