When it first was published in 1997, The Black Book of Communism: Crimes, Terror, Repression was obligatory reading for anybody who wanted to understand what Communism had just finished doing in the world. Most people thought Communism was finished at that point, though we are reminded by the cases of Cuba, North Korea, and the New York Times that it is not quite done.
Given what the calendar says today, this would be a good time to crack that book if you have not read it.