On the night of 21 May, two large earthquakes were followed by a collapse of the eastern flank of Mount Unzen's Mayuyama dome, causing a landslide which swept through the city of Shimabara and into Ariake Bay, triggering a great tsunami.
The 1792 Unzen earthquake and tsunami resulted from the volcanic activities of Mount Unzen (in the Shimabara Peninsula of Nagasaki Prefecture, Japan) on 21 May. This caused the collapse of the southern flank of the Mayuyama dome in front of Mount Unzen, resulting in a tremendous megatsunami, killing 15,000 people altogether.
On 21 May, the French made their first major effort to cross the Danube, precipitating the Battle of Aspern-Essling. The Austrians enjoyed a comfortable numerical superiority over the French throughout the battle. On the first day, Charles disposed of 110,000 soldiers against only 31,000 commanded by Napoleon. By the second day, reinforcements had boosted French numbers up to 70,000. It was the first defeat Napoleon suffered in a major set-piece battle, and it caused excitement throughout many parts of Europe because it proved that he could be beaten on the battlefield.
With the Federal Army defeated in a string of battles, Diaz's government began negotiations with the revolutionaries. One of Madero's representatives in the negotiations was his running mate in the 1910 elections, Francisco Vázquez Gómez. The talks culminated in the 21 May 1911 Treaty of Ciudad Juárez. The signed treaty stated that Díaz would abdicate the presidency along with his vice president Ramón Corral by the end of May 1911, to be replaced by an interim president, Francisco León de la Barra, until elections were held.
Ueno would commute daily to work, and Hachikō would leave the house to greet him at the end of each day at the nearby Shibuya Station. The pair continued the daily routine until May 21, 1925, when Ueno did not return. The professor had suffered a cerebral hemorrhage, while he was giving a lecture to his class, and died without ever returning to the train station in which Hachikō waited.
Doss was wounded four times in Okinawa and was evacuated on May 21, 1945, aboard the USS Mercy. Doss suffered a left arm fracture from a sniper's bullet and at one point had seventeen pieces of shrapnel embedded in his body. He was awarded the Medal of Honor for his actions in Okinawa.
21 May 1946: While conducting further impromptu experiments on the third plutonium core at Los Alamos National Laboratory, physicist Louis Slotin received a lethal dose of radiation. He died on 30 May 1946.
On May 21, 1962, Armstrong was involved in the "Nellis Affair". He was sent in an F-104 to inspect Delamar Dry Lake in southern Nevada, again for emergency landings. He misjudged his altitude, and did not realize that the landing gear had not fully extended. As he touched down, the landing gear began to retract; Armstrong applied full power to abort the landing, but the ventral fin and landing gear door struck the ground, damaging the radio and releasing hydraulic fluid. Without radio communication, Armstrong flew south to Nellis Air Force Base, past the control tower, and waggled his wings, the signal for a no-radio approach. The loss of hydraulic fluid caused the tailhook to release, and upon landing, he caught the arresting wire attached to an anchor chain, and dragged the chain along the runway.
Marley received a state funeral in Jamaica on 21 May 1981, which combined elements of Ethiopian Orthodoxy and Rastafari tradition. He was buried in a chapel near his birthplace with his guitar, and the Jamaican Prime Minister Edward Seaga delivered the final funeral eulogy to Marley.
During the night of 21 May, the British Amphibious Task Group under the command of Commodore Michael Clapp (Commodore, Amphibious Warfare – COMAW) mounted Operation Sutton, the amphibious landing on beaches around San Carlos Water, on the northwestern coast of East Falkland facing onto Falkland Sound.
On May 21, at Judgment Day, The Rock faced Triple H in an Iron Man match with Shawn Michaels as the special guest referee. With the score tied at five falls each, and with seconds left on the time limit, The Rock was disqualified when The Undertaker attacked Triple H, thus giving Triple H the 6–5 win and the title.
First Champions League title awarded. The 2008 UEFA Champions League Final was a football match that took place on Wednesday, 21 May 2008, at the Luzhniki Stadium in Moscow, Russia, to determine the winner of the 2007–08 UEFA Champions League. It was contested by Manchester United and Chelsea, making it an all-English club final for the first time in the history of the competition.
On May 21, 2009, it was announced that Ursula Burns would succeed Anne Mulcahy as CEO of Xerox. On July 1, 2009, Burns became the first African American woman to head a company the size of Xerox.
Until 2012, the King of Norway was, according to the constitution, the formal head of the Church of Norway. The constitutional amendment of 21 May 2012 made the King no longer the formal head, but he is still required to be of the Evangelical Lutheran religion.