- 1493 – Pope Alexander VI issued the papal bull Inter caetera, establishing a Line of Demarcation dividing the New World between Spain and Portugal.
- 1855 – American adventurer William Walker (pictured) and a group of mercenaries sailed from San Francisco to conquer Nicaragua.
- 1886 – An unknown assailant threw a bomb into a crowd of police, turning a peaceful labor rally in Chicago into the Haymarket massacre, resulting in the deaths of seven police officers and an unknown number of civilians.
- 1942 – World War II: The Imperial Japanese Navy engaged Allied naval forces at the Battle of the Coral Sea, the first fleet action in which aircraft carriers engaged each other, and the first naval battle in history in which neither side's ships sighted or fired directly upon the other.
- 1979 – Margaret Thatcher became the first female Prime Minister of the United Kingdom.
- 1990 – The Supreme Soviet of the Latvian SSR declared the restoration of independence of Latvia, stating that the Molotov-Ribbentrop Pact and the Soviet occupation of Latvia in 1940 were illegal.
