Don't we ever learn from history?
From The Black Book of Communism: Crimes, Terror, Repression.
The following rough approximation, based on unofficial estimates, gives some sense of the scale and gravity of these crimes:
U.S.S.R.: 20 million deaths
China: 65 million deaths
Vietnam: 1 million deaths
Cambodia: 2 million deaths
Eastern Europe: 1million deaths
Latin America: 150,000 deaths
Africa: 1.7million deaths
Afghanistan: 1.5 million deaths
The international Communist movement and Communist parties not in power: about 10,000 deaths
The total approaches 100 million people killed.