Wikipedia:Selected anniversaries/August 20
August 20: St. Stephen's Day in Hungary
- 917 - Tsar Simeon I of Bulgaria invaded Thrace and drove the Byzantines out.
- 1882 - Pyotr Ilyich Tchaikovsky's "1812 Overture" debuted in Moscow.
- 1968 - 200,000 Warsaw Pact troops and 5,000 tanks invaded Czechoslovakia to end the "Prague Spring" of political liberalization.
- 1977 - Voyager 2 lifted off from Cape Canaveral, Florida on a mission to explore the outer planets of the solar system.
- 1991 - Estonia regained its independence in the Singing Revolution as part of the collapse of the Soviet Union.