大躍進. The Great Leap Forward (1958-1962)… estimated to have caused between 15 and 55 million deaths…

無產階級文化大革命. The Cultural Revolution (1966-1976)… estimated death toll ranging from hundreds of thousands to 20 million…

八九民運. The Tiananmen Square Massacre (April 15, 1989 – June 4, 1989)… estimates ranged from the official figure of a few hundred to several thousand.

Would seem to be China itself…