May 1: International Workers' Day; Beltane and Samhain in the Northern and Southern Hemispheres, respectively; Maharashtra Day in Maharashtra, India (1960); Loyalty Day in the United States
Scene from Citizen Kane
- 1707 – Under the terms of the Acts of Union, the Kingdoms of England and Scotland merged to form the Kingdom of Great Britain, with a single parliament and government based in Westminster.
- 1941 – Citizen Kane (scene pictured), a widely acclaimed film by actor and director Orson Welles, premiered.
- 1991 – In Major League Baseball, Rickey Henderson broke the record for stolen bases on the same night that Nolan Ryan broke his own record for no-hitters.
- 2016 – The evacuation of nearly 88,000 people began when a wildfire swept through Fort McMurray, Alberta, Canada, and burned for another 14 months, becoming the costliest disaster in Canadian history.
May 2: Flag Day in Poland
May 3: World Press Freedom Day; Constitution Memorial Day in Japan (1947); Constitution Day in Poland (1791)
Benty Grange helmet
- 1491 – Nkuwu Nzinga, the ruler of the Kingdom of Kongo, was baptised as João I by Portuguese missionaries.
- 1848 – The Benty Grange helmet (pictured), a boar-crested Anglo-Saxon helmet similar to those mentioned in the contemporary epic poem Beowulf, was discovered in Derbyshire, England.
- 1921 – Under the British Government of Ireland Act, Ireland was partitioned into two self-governing territories, Northern and Southern Ireland.
- 1963 – Police in Birmingham, Alabama, used high-pressure water hoses and dogs against civil-rights protesters, bringing scrutiny on racial segregation in the southern United States.
- 1971 – Erich Honecker became First Secretary of the Socialist Unity Party of Germany, the governing party of East Germany.
May 4: Star Wars Day
May 5: Children's Day in Japan; Cinco de Mayo in Mexico and the United States (1862)
Alan Shepard on board Freedom 7
May 6: National Day of Prayer in the United States (2021)
Alexander Stepanovich Popov
May 8: World Red Cross and Red Crescent Day; Pesach Sheni (Judaism, 2020); Anniversary of the birth of Miguel Hidalgo in Mexico (1753); Victory in Europe Day (1945)
Sketch of the Versailles rail accident
May 9: Europe Day / Schuman Day in the European Union; Victory Day in various Eastern European countries; Liberation Day in the Channel Islands (1945)
- 1833 – Siamese–Vietnamese wars: Lê Văn Khôi escaped from prison to begin a revolt against Emperor Minh Mạng, primarily to avenge his adoptive father, Vietnamese general Lê Văn Duyệt.
- 1916 – Ernest Shackleton and five companions arrived at South Georgia, completing a 1,300 km (800 mi) lifeboat voyage (launch pictured) over 16 days to obtain rescue for the Imperial Trans-Antarctic Expedition.
- 1997 – An earthquake registering 7.3 Mw struck near Qaen, Iran, killing at least 1,567 and leaving around 50,000 others homeless.
- 2013 – The final component of the spire of One World Trade Center in New York City was installed, bringing the building, the tallest in the Western Hemisphere, to a height of 1,776 feet (541 m).
Crossing of the Blue Mountains
May 12: Lag BaOmer (Judaism, 2020)
May 14: Feast day of Saint Matthias (Catholicism)
May 15: Feast day of Saint Carthage (Irish Catholicism); Nakba Day in Palestinian communities; Sanja Matsuri begins in Tokyo (2020)
May 16: Night of Decree (Shia Islam, 2020)
Theodore Maiman with his laser
May 17: Galician Literature Day in Galicia, Spain
May 18: Victoria Day in Canada (2020); Flag and Universities Day in Haiti (1803); Day of Revival, Unity, and the Poetry of Magtymguly in Turkmenistan (1733)
Eruption of Mount St. Helens
May 19: Pontian Greek Genocide Remembrance Day in Greece (1919); Commemoration of Atatürk, Youth and Sports Day in Turkey (1919)
May 20: Night of Decree (Sunni Islam, 2020); National Day of Remembrance in Cambodia (1976); National Day in Cameroon (1972)
Abraham Ortelius's world map
Richard Loeb (left) and Nathan Leopold (right)
May 22: International Day for Biological Diversity; International Quds Day (2020); Jerusalem Day in Israel (2020)
Blackwall Tunnel under construction
May 23: Aromanian National Day
May 24: Eid al-Fitr (Islam, 2020); Aldersgate Day (Methodism)
Patrick Francis Healy
May 25: Africa Day (1963); Anniversary of the First National Government in Argentina (1810); Independence Day in Jordan (1946); Memorial Day in the United States (2020)
May 26: Independence Day in Georgia (1918)
May 27: Qibla observation by shadows (09:18 UTC, Islam)
May 28: Republic Day in Azerbaijan (1918)
Bust of Louis Delgrès
- 1802 – In an attempt to resist the reintroduction of slavery in Guadeloupe, Louis Delgrès (bust pictured) and hundreds of his followers blew themselves up, killing many French troops in the process.
- 1892 – Scottish-American preservationist John Muir founded the environmental organization Sierra Club in San Francisco, California.
- 1901 – Mozaffar ad-Din, the shah of Persia, granted exclusive rights to prospect for oil in the country to William Knox D'Arcy.
- 1987 – Mathias Rust, a West German aviator, flew his Cessna 172 from Helsinki, Finland, through Soviet air defences, landing illegally near Red Square in Moscow.
- 2010 – A train derailment and collision in the West Midnapore district of West Bengal, India, caused the deaths of at least 148 passengers.
May 29: First day of Shavuot (Judaism, 2020); feast day of Saint Paul VI (Catholicism)
Place de la Nation, N'Djamena
May 30: Lod Massacre Remembrance Day in Puerto Rico (1972); Statehood Day in Croatia
Auckland Harbour Bridge
May 31: World No Tobacco Day
- 1223 – Mongol invasion of Kievan Rus': Mongol forces defeated a combined Rus' army at the Kalka River in present-day Ukraine.
- 1775 – American Revolution: The Committee of Safety of Mecklenburg County, North Carolina, adopted the Mecklenburg Resolves, which annulled and vacated all laws originating from the authority of the King or Parliament.
- 1902 – The Second Boer War came to an end with the signing of the Treaty of Vereeniging in Pretoria, South Africa.
- 1935 – An earthquake registering 7.7 Mw struck Balochistan in the British Raj, now part of Pakistan, killing between 30,000 and 60,000 people.
- 2005 – An article in the magazine Vanity Fair revealed that the secret informant known as "Deep Throat", who had provided information about the Watergate scandal, was former FBI associate director Mark Felt (pictured).