On May 21

The Greenfield tornado, estimated to have produced winds in excess of 309 miles per hour (497 km/h), moves across Iowa.

Islamic State militants entered the ancient city of Palmyra.

A Taiwanese man carried out a stabbing spree on a Taipei Metro train, killing four people and injuring 24 others.

The world's tallest roller coaster, Kingda Ka, opened at Six Flags Great Adventure in Jackson, New Jersey, U.S.

Indonesian president Suharto resigned after a collapse of support for his presidency amid economic and political crises, ending 32 years in power.

Former Indian prime minister Rajiv Gandhi was assassinated by a suicide bomber in Sriperumbudur, Tamil Nadu.

While working with a mass of plutonium known as the demon core, Manhattan Project physicist Louis Slotin accidentally exposed himself to a lethal dose of hard radiation.

Aboard the Spirit of St. Louis, American aviator Charles Lindbergh (pictured) completed the first solo non-stop transatlantic flight, flying from Roosevelt Field near New York City to Paris–Le Bourget Airport.

The opera Doktor Faust, unfinished when composer Ferruccio Busoni (pictured) died, was premiered in Dresden.

University of Chicago students Nathan Leopold Jr. and Richard Loeb (both pictured) murdered a 14-year-old boy in a thrill killing out of a desire to commit a "perfect crime".

The Imperial War Graves Commission was established by royal charter to mark, record and maintain the graves and places of commemoration of British Empire military forces.

Mexican president Porfirio Díaz and the revolutionary Francisco I. Madero signed the Treaty of Ciudad Juárez to end hostilities between each other's forces, concluding the initial phase of the Mexican Revolution.

The Manchester Ship Canal, linking Manchester in North West England to the Irish Sea, officially opened, becoming the world's largest navigation canal at the time.

American Civil War: The inconclusive Battle of Spotsylvania Court House in Virginia ended with combined Union and Confederate casualties totaling around 31,000.

A crowd of about 800 pro-slavery Americans ransacked the town of Lawrence, Kansas.

The Congress of Colombia passed a law abolishing slavery in the country, to take effect at the beginning of the new year.

English writer Daniel Defoe was imprisoned for seditious libel after publishing a pamphlet that was perceived to satirise the Tory publications about Dissenters.

The Crusades: The siege of Shaizar ended, and the Emir of Shaizar became a vassal of the Byzantine Empire.

Arab–Byzantine wars: The city of Syracuse was captured by the Aghlabids (pictured) as part of the Muslim conquest of Sicily.