History of the Day for:
May 21
- 1542: Spanish explorer Hernando de Soto died while searching for gold along the Mississippi River.
- 1832: The first Democratic National Convention was held in Baltimore.
- 1840: New Zealand became a British colony.
- 1881: Clara Barton founded the American Red Cross.
- 1892: In Milan, Italy, the opera "I Pagliacci," written by Ruggiero Leoncavallo, was first performed.
- 1924: Fourteen-year-old Bobby Franks was murdered by University of Chicago students Nathan Leopold Jr. and Richard Loeb.
- 1927: Charles A. Lindbergh, in his "Spirit of St. Louis," landed near Paris, completing the first solo airplane flight across the Atlantic Ocean.
- 1945: Lauren Bacall and Humphrey Bogart were married.
- 1956: The United States exploded the first airborne hydrogen bomb over Bikini Atoll in the Pacific.
- 1959: With Ethel Merman in the leading role, the musical "Gypsy" opened on Broadway.
- 1968: The nuclear-powered submarine Scorpion, with 99 men, lost contact and was later found at the bottom of the ocean.
- 1979: Former San Francisco City Supervisor Dan White was convicted of voluntary manslaughter in the slayings of Mayor George Moscone and Supervisor Harvey Milk. White used the "Twinkie" defense.
- 1991: Former Indian Prime Minister Rajiv Gandhi was assassinated by a suicide bomber.
- 1994: The Democratic Republic of Yemen secedes from the Republic of Yemen.
- 1996: The MV Bukoba sinks in Tanzanian waters on Lake Victoria, killing nearly 1000.
- 1996: The Trappist Martyrs of Atlas are executed.
- 1998: In Miami, Florida, five abortion clinics are hit by a butyric acid attacker.
- 1998: Suharto, the Indonesian dictator who had ruled for 32 years, resigns.
- 2001: French Taubira law officially recognizes the Atlantic slave trade and slavery as crimes against humanity.
- 2003: An earthquake hits northern Algeria killing more than 2,000 people.
- 2004: Sherpa Pemba Dorjie climbs Mount Everest in 8 hours 10 minutes, breaking his rival Sherpa Lakpa Gelu's record from the previous year.
- 2006: The Republic of Montenegro holds a referendum proposing independence from the State Union of Serbia and Montenegro. The Montenegrin people choose independence with a majority of 55%.
- 2006: The Swedish ice hockey team Tre Kronor takes gold in the World Championship, becoming the first nation to hold both the World and Olympic titles separately in the same year.
- 2007: The clipper Cutty Sark is badly damaged by fire in London, England.