Excerpt from this article: "According to “The Black Book of Communism: Crimes, Terror, Repression,” a text considered the standard recollection of the USSR’s atrocities, 20 million perished as a result of Stalin’s targeted killings, forced labor, famine, and collectivization. These numbers were confirmed by a major Soviet newspaper in 1989...An estimate cited by the libertarian magazine Reason puts the total number of people killed because of communism from 1900 to 2000 at a staggering 94 million — making it by far the bloodiest ideology in recent history."
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For further study...None Dare Call it Conspiracy, by Gary Allen (1971)