August 21
- 1192 - Minamoto Yoritomo becomes Seii Tai Shōgun and the de facto ruler of Japan. (Traditional Japanese date: July 12, 1192).
- 1680 - Pueblo Indians capture Santa Fe from Spanish during the Pueblo Revolt.
- 1852 - Tlingit Indians destroy Fort Selkirk, Yukon Territory.
- 1968 - Soviet Union-dominated Warsaw Pact troops invade Czechoslovakia, crushing the Prague Spring; on the same day, Nicolae Ceaușescu, leader of Communist Romania, publicly condemns the Soviet maneuver, encouraging the Romanian population to arm itself against possible Soviet reprisals.
August 21
- 1192 - Minamoto Yoritomo becomes Seii Tai Shōgun and the de facto ruler of Japan. (Traditional Japanese date: July 12, 1192).
- 1680 - Pueblo Indians capture Santa Fe from Spanish during the Pueblo Revolt.
- 1852 - Tlingit Indians destroy Fort Selkirk, Yukon Territory.
- 1968 - Soviet Union-dominated Warsaw Pact troops invade Czechoslovakia, crushing the Prague Spring; on the same day, Nicolae Ceaușescu, leader of Communist Romania, publicly condemns the Soviet maneuver, encouraging the Romanian population to arm itself against possible Soviet reprisals.