[pasabagi]

World population circa 1950 was like 2 billion. I don't know what the root study is that reaches that 100M figure, but the idea that communism killed one in twenty people on the whole planet seems a bit unlikely.

The really high end figures for the worst[0] man-made disaster of all time (the famine during the great leap forward) are 42 million, no idea where you'd get the rest of the numbers from.

[0]: edit: I thought it was the worst: apparently there were several previous famines in China in the 19th century that were more deadly.