- 1027 – Robert II of France names his son Henry I as junior King of the Franks.
- 1097 – The Siege of Nicaea begins during the First Crusade.
- 1264 – Battle of Lewes: Henry III of England is captured and forced to sign the Mise of Lewes, making Simon de Montfort the effective ruler of England.
- 1509 – Battle of Agnadello: In northern Italy, French forces defeat the Republic of Venice.
- 1607 – English colonists establish "James Fort," which would become Jamestown, Virginia, the earliest permanent English settlement in the Americas.
- 1608 – The Protestant Union, a coalition of Protestant German states, is founded to defend the rights, land and safety of each member against the Catholic Church and Catholic German states.
- 1610 – Henry IV of France is assassinated by Catholic zealot François Ravaillac, and Louis XIII ascends the throne.
- 1643 – Four-year-old Louis XIV becomes King of France upon the death of his father, Louis XIII.
- 1747 – War of the Austrian Succession: A British fleet under Admiral George Anson defeats the French at the First Battle of Cape Finisterre.
- 1796 – Edward Jenner administers the first smallpox inoculation.
- 1800 – The 6th United States Congress recesses, and the process of moving the Federal government of the United States from Philadelphia to Washington, D.C., begins the following day.
- 1804 – William Clark and 42 men depart from Camp Dubois to join Meriwether Lewis at St Charles, Missouri, marking the beginning of the Lewis & Clark Expedition's historic journey up the Missouri River.
- 1811 – Paraguay: Pedro Juan Caballero, Fulgencio Yegros and José Gaspar Rodríguez de Francia start actions to depose the Spanish governor.
- 1836 – The Treaties of Velasco are signed in Velasco, Texas.
- 1863 – American Civil War: The Battle of Jackson takes place.
- 1868 – Boshin War: The Battle of Utsunomiya Castle ends as former Tokugawa shogunate forces withdraw northward.
- 1870 – The first game of rugby in New Zealand is played in Nelson between Nelson College and the Nelson Rugby Football Club.
- 1878 – The last witchcraft trial held in the United States begins in Salem, Massachusetts, after Lucretia Brown, an adherent of Christian Science, accused Daniel Spofford of attempting to harm her through his mental powers.
- 1879 – The first group of 463 Indian indentured laborers arrives in Fiji aboard the Leonidas.
- 1900 – Opening of World Amateur championship at the Paris Exposition Universelle, also known as Olympic Games. 
- 1913 – Governor of New York William Sulzer approves the charter for the Rockefeller Foundation, which begins operations with a $100 million donation from John D. Rockefeller.
- 1915 – The May 14 Revolt takes place in Lisbon, Portugal.
- 1918 – Cape Town Mayor, Sir Harry Hands, inaugurates the Two-minute silence.
- 1931 – Five unarmed civilians are killed in the Ådalen shootings, as the Swedish military is called in to deal with protesting workers.
- 1935 – The Constitution of the Philippines is ratified by a popular vote.
- 1939 – Lina Medina becomes the youngest confirmed mother in medical history at the age of five.
- 1940 – World War II: Rotterdam, Netherlands is bombed by the Luftwaffe of Nazi Germany despite a ceasefire, killing about 900 people and destroying the historic city center.
- 1943 – World War II: A Japanese submarine sinks AHS Centaur off the coast of Queensland.
- 1948 – Israel is declared to be an independent state and a provisional government is established. Immediately after the declaration, Israel is attacked by the neighboring Arab states, triggering the 1948 Arab–Israeli War.
- 1951 – Trains run on the Talyllyn Railway in Wales for the first time since preservation, making it the first railway in the world to be operated by volunteers.
- 1953 – Approximately 7,100 brewery workers in Milwaukee perform a walkout, marking the start of the 1953 Milwaukee brewery strike.
- 1955 – Cold War: Eight Communist bloc countries, including the Soviet Union, sign a mutual defense treaty called the Warsaw Pact.
- 1961 – Civil rights movement: A white mob twice attacks a Freedom Riders bus near Anniston, Alabama, before fire-bombing the bus and attacking the civil rights protesters who flee the burning vehicle.
- 1970 – Andreas Baader is freed from custody by Ulrike Meinhof, Gudrun Ensslin and others, a pivotal moment in the formation of the Red Army Faction.
- 1973 – Skylab, the United States' first space station, is launched.
- 1977 – A Dan-Air Boeing 707 leased to IAS Cargo Airlines crashes on approach to Lusaka International Airport in Lusaka, Zambia, killing six people.
- 1980 – Salvadoran Civil War: the Sumpul River massacre occurs in Chalatenango, El Salvador.
- 1988 – Carrollton bus collision: A drunk driver traveling the wrong way on Interstate 71 near Carrollton, Kentucky hits a converted school bus carrying a church youth group. Twenty-seven die in the crash and ensuing fire.
- 2004 – The Constitutional Court of South Korea overturns the impeachment of President Roh Moo-hyun.
- 2004 – Rico Linhas Aéreas Flight 4815 crashes into the Amazon rainforest during approach to Eduardo Gomes International Airport in Manaus, Brazil, killing 33 people.
- 2008 – Battle of Piccadilly Gardens in Manchester city centre between Zenit supporters and Rangers supporters and the Greater Manchester Police, 39 policemen injured, one police-dog injured and 39 arrested.
- 2010 – Space Shuttle Atlantis launches on the STS-132 mission to deliver the first shuttle-launched Russian ISS component — Rassvet. This was originally slated to be the final launch of Atlantis, before Congress approved STS-135.
- 2012 – Agni Air Flight CHT crashes in Nepal after a failed go-around, killing 15 people.
Holidays and observances
- Christian feast day:
- Earliest day on which the first day of Sanja Matsuri can fall, while May 21 is the latest; celebrated on the third weekend of May. (Sensō-ji, Tokyo)
- Flag Day (Paraguay)
- Hastings Banda's Birthday (Malawi)
- National Unification Day (Liberia)
- The first day of Izumo-taisha Shrine Grand Festival. (Izumo-taisha)