The Great Purge was a campaign of political repression and persecution in the Soviet Union from 1936 to 1938, ordered by Joseph Stalin.

Adolf Hitler was the leader of the Nazi Party and Chancellor of Germany from 1933 to 1945.

The Cambodian genocide was a systematic genocide of the Cambodian people carried out by the Khmer Rouge regime from 1975 to 1979.

The Gestapo was the official secret police of Nazi Germany.

The Cultural Revolution was a sociopolitical movement in the People's Republic of China from 1966 to 1976, led by Mao Zedong.

The NKVD was the official secret police of the Soviet Union.

The Holodomor was a man-made famine in Ukraine from 1932 to 1933, caused by the policies of Joseph Stalin.

The OVRA was the official secret police of Fascist Italy.

The Rape of Nanking was a mass rape and murder of Chinese civilians by the Imperial Japanese Army during the Second Sino-Japanese War.

The Kempeitai was the official secret police of Imperial Japan.

The Katyn Forest Massacre was the mass execution of Polish prisoners of war by the Soviet Union in 1940.

Franco's Spain did not have a secret police.

The Tiananmen Square Massacre was a mass shooting of pro-democracy protesters in Beijing, China, in 1989.

North Korea does not have a secret police.

The Great Leap Forward was a campaign in the People's Republic of China from 1958 to 1962, aimed at rapidly industrializing the country.