May 21 events in history

293 Roman Emperors Diocletian and Maximian appoint Galerius as Caesar to Diocletian, beginning the period of four rulers known as the Tetrarchy
878 Syracuse, Sicily, is captured by the Muslim sultan of Sicily
879 Pope John VIII gives blessings to Branimir of Croatia and to the Croatian people, considered to be international recognition of the Croatian state
996 Sixteen-year-old Otto III is crowned Holy Roman Emperor
1085 The Swedish town of Helsingborg is founded
1349 Dušan's Code, the constitution of the Serbian Empire, is enacted by Dušan the Mighty
1403 Henry III of Castile sends Ruy Gonzáles de Clavijo as ambassador to Timur to discuss the possibility of an alliance between Timur and Castile against the Ottoman Empire
1502 The island of Saint Helena is discovered by the Portuguese explorer João da Nova
1554 Queen Mary I grants a royal charter to Derby School, as a grammar school for boys in Derby, England
1674 The nobility elect John Sobieski King of Poland and Grand Duke of Lithuania
1725 The Order of St. Alexander Nevsky is instituted in Russia by Empress Catherine I. It would later be discontinued and then reinstated by the Soviet government in 1942 as the Order of Alexander Nevsky
1758 Ten-year-old Mary Campbell is abducted in Pennsylvania by Lenape during the French and Indian War. She is returned six and a half years later
1809 The first day of the Battle of Aspern-Essling between the Austrian army led by Archduke Charles and the French army led by Napoleon I of France sees the French attack across the Danube held
1851 Slavery is abolished in Colombia, South America
1856 Lawrence, Kansas is captured and burned by pro-slavery forces
1863 American Civil War: The Union Army succeeds in closing off the last escape route from Port Hudson, Louisiana, in preparation for the coming siege
1863 Organization of the Seventh-day Adventist Church in Battle Creek, Michigan
1864 Russia declares an end to the Russian–Circassian War and many Circassians are forced into exile. The day is designated the Circassian Day of Mourning
1864 American Civil War: the Battle of Spotsylvania Court House ends
1871 French troops invade the Paris Commune and engage its residents in street fighting. By the close of "Bloody Week", some 20,000 communards have been killed and 38,000 arrested
1871 Opening of the first rack railway in Europe, the Rigi-Bahnen on Mount Rigi
1879 War of the Pacific: Two Chilean ships blocking the harbor of Iquique (then belonging to Peru) battle two Peruvian vessels in the Battle of Iquique
1881 The American Red Cross is established by Clara Barton in Washington, D.C
1894 The Manchester Ship Canal in the United Kingdom is officially opened by Queen Victoria, who later knights its designer Sir Edward Leader Williams
1904 The Fédération Internationale de Football Association (FIFA) is founded in Paris
1911 President of Mexico Porfirio Díaz and the revolutionary Francisco Madero sign the Treaty of Ciudad Juárez to put an end to the fighting between the forces of both men, concluding the initial phase of the Mexican Revolution
1917 The Commonwealth War Graves Commission is established through royal charter to mark, record and maintain the graves and places of commemoration of Commonwealth of Nations military forces
1917 The Great Atlanta fire of 1917 causes $5.5 million in damages, destroying some 300 acres including 2,000 homes, businesses and churches, displacing about 10,000 people but leading to only one fatality (due to heart attack)
1924 University of Chicago students Richard Loeb and Nathan Leopold, Jr. murder 14-year-old Bobby Franks in a "thrill killing"
1927 Charles Lindbergh touches down at Le Bourget Field in Paris, completing the world's first solo nonstop flight across the Atlantic Ocean
1932 Bad weather forces Amelia Earhart to land in a pasture in Derry, Northern Ireland, and she thereby becomes the first woman to fly solo across the Atlantic Ocean
1934 Oskaloosa, Iowa, becomes the first municipality in the United States to fingerprint all of its citizens
1936 Sada Abe is arrested after wandering the streets of Tokyo for days with her dead lover's severed genitals in her handbag. Her story soon becomes one of Japan's most notorious scandals
1937 A Soviet station, North Pole-1, becomes the first scientific research settlement to operate on the drift ice of the Arctic Ocean
1939 The Canadian National War Memorial is unveiled by King George VI and Queen Elizabeth in Ottawa
1946 Physicist Louis Slotin is fatally irradiated in a criticality incident during an experiment with the demon core at Los Alamos National Laboratory
1951 The opening of the Ninth Street Show, otherwise known as the 9th Street Art Exhibition – a gathering of a number of notable artists, and the stepping-out of the post war New York avant-garde, collectively known as the New York School
1961 American civil rights movement: Alabama Governor John Malcolm Patterson declares martial law in an attempt to restore order after race riots break out
1966 The Ulster Volunteer Force declares war on the Irish Republican Army in Northern Ireland
1969 Civil unrest in Rosario, Argentina, known as Rosariazo, following the death of a 15-year-old student
1972 Michelangelo's Pietà in St. Peter's Basilica in Rome is damaged by a vandal, the mentally disturbed Hungarian geologist Laszlo Toth
1976 The Yuba City bus disaster occurs in Martinez, California. Twenty-nine are killed making it the deadliest road accident in U.S. history
1979 White Night riots in San Francisco following the manslaughter conviction of Dan White for the assassinations of George Moscone and Harvey Milk
1981 Irish Republican hunger strikers Raymond McCreesh and Patsy O'Hara die on hunger strike in Maze prison
1981 The Italian government releases the membership list of Propaganda Due, an illegal pseudo-Masonic lodge that was implicated in numerous Italian crimes and mysteries
1982 Falklands War: A British amphibious assault during Operation Sutton leads to the Battle of San Carlos
1991 Former Indian Prime Minister Rajiv Gandhi is assassinated by a female suicide bomber near Madras
1991 Mengistu Haile Mariam, president of the People's Democratic Republic of Ethiopia, flees Ethiopia, effectively bringing the Ethiopian Civil War to an end
1992 After 30 seasons Johnny Carson hosted his penultimate episode and last featuring guests (Robin Williams and Bette Midler) of The Tonight Show
1994 The Democratic Republic of Yemen unsuccessful attempts to secede from the Republic of Yemen; a war breaks out