History of the Day for:
March 15
- 44 B.C.: Roman dictator Julius Caesar was assassinated by a group of nobles that included Brutus and Cassius.
- 1493: Christopher Columbus returned to Spain, concluding his first voyage to the Western Hemisphere.
- 1767: The seventh president of the United States, Andrew Jackson, was born in Waxhaw, S.C.
- 1820: Maine became the 23rd state.
- 1875: The Roman Catholic Archbishop of New York, John McCloskey, was named the first American cardinal, by Pope Pius the Ninth.
- 1913: President Wilson held the first open presidential news conference; President Woodrow Wilson held the first open presidential news conference.
- 1919: The American Legion was founded in Paris.
- 1937: The first blood bank was established in Chicago at the Cook County Hospital.
- 1939: World War II: German troops occupy the remaining part of Bohemia and Moravia; Czechoslovakia ceases to exist.
- 1943: World War II: Third Battle of Kharkov – the Germans retake the city of Kharkov from the Soviet armies in bitter street fighting.
- 1944: World War II: Battle of Monte Cassino – Allied aircraft bomb the German-held monastery and stage an assault.
- 1945: "Going My Way," starring Bing Crosby, won an Academy Award for Best Film and an Oscar for Crosby, who played a priest. These Oscar awards were the first broadcast in entirety over the ABC Radio Network and Armed Forces Radio around the world.
- 1952: In Cilaos, Réunion, 1870 mm (73 inches) of rain falls in one day, setting a new world record.
- 1956: The Lerner and Loewe musical "My Fair Lady" opened on Broadway.
- 1962: Wilt Chamberlain became the first and only player in NBA history to score more than 4,000 points in a season (4,029). He averaged 50.4 points per game.
- 1971: CBS announced it was dropping "The Ed Sullivan Show" from its program lineup after 23 years.
- 1985: The first Internet domain name is registered (symbolics.com).
- 1988: The Halabja poison gas attack of the Iran–Iraq War begins.
- 1989: The United States Department of Veterans Affairs is established.
- 1990: Gulf War: Iraq hangs British journalist Farzad Bazoft for spying.
- 1990: Mikhail Gorbachev is elected as the first executive president of the Soviet Union.
- 1990: The ethnic clashes of Târgu Mures begin on the anniversary of the Revolutions of 1848 in the Habsburg areas.