| | Cvp: On This Day... Events (May 20th) - 325 - The First Council of Nicaea – the first Ecumenical Council of the Christian Church – is held.
- 526 - An earthquake kills about 300,000 people in Syria and Antiochia.
- 685 - The Battle of Dunnichen or Nechtansmere is fought between a Pictish army under King Bridei III and the invading Northumbrians under King Ecgfrith, who are decisively defeated.
- 1217 - The Second Battle of Lincoln is fought near Lincoln, England, resulting in the defeat of Prince Louis of France by William Marshal, 2nd Earl of Pembroke.
- 1293 - King Sancho IV of Castile creates the Study of General Schools of Alcalá.
- 1497 - John Cabot sets sail from Bristol, England, on his ship Matthew looking for a route to the west (other documents give a 2 May date).
- 1498 - Portuguese explorer Vasco da Gama arrives at Kozhikode (previously known as Calicut), India.
- 1521 - Battle of Pampeluna: Ignatius Loyola seriously wounded in the battle.
- 1570 - Cartographer Abraham Ortelius issues the first modern atlas.
- 1631 - The city of Magdeburg in Germany is seized by forces of the Holy Roman Empire and most of its inhabitants massacred, in one of the bloodiest incidents of the Thirty Years' War.
- 1690 - England passes the Act of Grace, forgiving followers of Roman Catholic James II.
- 1813 - Napoleon Bonaparte leads his French troops into the Battle of Bautzen in Saxony, Germany, against the combined armies of Russia and Prussia. The battle ends the next day with a French victory.
- 1835 - Otto is named the first modern king of Greece.
- 1845 - HMS Erebus and HMS Terror with 134 men under John Franklin sail from the River Thames in England, beginning a disastrous expedition to find the Northwest Passage. All hands are lost.
- 1861 - American Civil War: The state of Kentucky proclaims its neutrality, which will last until September 3 when Confederate forces enter the state.
- 1862 - U.S. President Abraham Lincoln signs the Homestead Act into law.
- 1864 - American Civil War: Battle of Ware Bottom Church - In the Virginia Bermuda Hundred Campaign, 10,000 troops fight in this Confederate victory.
- 1873 - Levi Strauss and Jacob Davis receive a U.S. patent for blue jeans with copper rivets.
- 1882 - The Triple Alliance between Germany, Austria-Hungary and Italy is formed.
- 1883 - The eruption of Krakatoa begins, leading ultimately to the volcano's destruction three months later.
- 1891 - History of cinema: First public display of Thomas Alva Edison's prototype kinetoscope (shown at Edison's Laboratory for a convention of the National Federation of Women's Clubs).
- 1896 - The six ton chandelier of the Palais Garnier falls on the crowd resulting in the death of one and the injury of many others.
- 1902 - Cuba gains independence from the United States. Tomás Estrada Palma becomes the first President of Cuba.
- 1910 - Krazy Kat and Ignatz first appear in 'The Dingbat Family' comic strip
- 1916 - The Saturday Evening Post publishes its first cover with a Norman Rockwell painting ("Boy with Baby Carriage").
- 1916 - The small town of Codell, Kansas is struck by a tornado. Incredibly, the same town was also hit in 1917 and 1918 on the exact same date
- 1920 - The Weimarer Nationalversammlung, the national assembly of Germany's Weimar Republic, is permanently dissolved.
- 1920 - Montreal Quebec station XWA broadcasts the first regularly scheduled radio programming in North America.
- 1927 - By the Treaty of Jedda, the United Kingdom recognizes the sovereignty of King Ibn Saud in the Kingdoms of Hejaz and Nejd, which later merged to become the Kingdom of Saudi Arabia.
- 1927 - At 07:52 Charles Lindbergh takes off from Roosevelt Field in Long Island, New York, on the world's first solo nonstop flight across the Atlantic Ocean, touching down at Le Bourget Field in Paris at 22:22 the next day.
- 1932 - Amelia Earhart takes off from Newfoundland to begin the world's first solo nonstop flight across the Atlantic Ocean by a female pilot, landing in Ireland the next day.
- 1940 - Holocaust: The first prisoners arrive at a new concentration camp at Auschwitz.
- 1941 - World War II: Battle of Crete – German paratroops invade Crete.
- 1949 - In the United States of America, the Armed Forces Security Agency (predecessor to the National Security Agency) is established.
- 1949 - Kuomintang regime declare Taiwan is under the martial law.
- 1954 - Chiang Kai-shek is selected for another term as President of the Republic of China by the National Assembly.
- 1965 - PIA Flight 705, a Pakistan International Airlines Boeing 720 - 040 B crashes while descending to land at Cairo International Airport, killing 119 of the 125 passengers and crew.
- 1969 - The Battle of Hamburger Hill in Vietnam ends.
- 1980 - In a Referendum in Quebec, the population rejects by a 60% vote the proposal from its government to move towards independence from Canada.
- 1983 - First publications of the discovery of the virus that causes AIDS in the journal Science by Luc Montagnier and Robert Gallo individually.
- 1984 - The first line of the Miami Metrorail in Miami, Florida opens.
- 1985 - Radio Martí, part of the Voice of America service, begins broadcasting to Cuba.
- 1989 - The Chinese authorities declare martial law in the face of pro-democracy demonstrations, setting the scene for the Tiananmen Square massacre.
- 1990 - The first post-Communist presidential and parliamentary elections are held in Romania.
- 1995 - In a second Referendum in Quebec, the population rejects by a slight majority the proposal from its government to move towards independence from Canada.
- 1996 - Gay rights: The Supreme Court of the United States rules in Romer v. Evans against a law that would have prevented any city, town or county in the state of Colorado from taking any legislative, executive, or judicial action to protect the rights of gays and lesbians.
- 2002 - East Timor becomes independent from Indonesian rule.
Events (May 21st) - 878 - Syracuse is captured by the Muslim sultan of Sicily.
- 879 - Pope John VIII gives blessings to duke Branimir and to Croatian people, considered to be international recognition of Croatian state
- 996 - Sixteen-year-old Otto III is crowned Holy Roman Emperor.
- 1502 - The island of Saint Helena is discovered by the Portuguese navigator João da Nova.
- 1674 - John Sobieski is elected by the szlachta to be the King of Poland.
- 1725 - The Order of St. Alexander Nevsky was instituted in Russia by an empress Catherine I. It would later be discontinued and then reinstated by the Soviet government in 1942 as the Order of Alexander Nevsky.
- 1758 - Mary Campbell is abducted from her home in Pennsylvania by Lenape during the French and Indian War.
- 1851 - Abolition of slavery in Colombia, South America.
- 1856 - Lawrence, Kansas is captured and burned by pro-slavery forces.
- 1863 - American Civil War: Siege of Port Hudson – Union forces begin to lay siege to the Confederate-controlled Port Hudson, Louisiana.
- 1871 - French Government 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.
- 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.
- 1894 - The Manchester Ship Canal in England is officially opened by Queen Victoria, who knights its designer Sir Edward Leader Williams.
- 1894 - 22-year-old French Anarchist Emile Henry is executed by guillotine.
- 1904 - Fédération Internationale de Football Association (FIFA) founded in Paris.
- 1917 - Great Atlanta fire of 1917.
- 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 - Amelia Earhart, because of bad weather, lands in a pasture in Derry, Northern Ireland, becoming the first woman to fly solo across the Atlantic Ocean.
- 1934 - Oskaloosa, Iowa, becomes the first municipality in the United States to fingerprint each 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 hand. Her story soon became one of Japan's most notorious scandals.
- 1937 - a Soviet station becomes the first scientific research settlement to operate on the drift ice of the Arctic Ocean.
- 1941 - World War II: 950 miles off the coast of Brazil, the freighter SS Robin Moor becomes the first United States ship sunk by a German U-boat.
- 1945 - United States screen legend Humphrey Bogart marries actress Lauren Bacall.
- 1951 - opening of the Ninth Street Show otherwise known as the 9th Street Art Exhibition was a gathering of a number of notable artists, and it was the stepping-out of the post war New York avant-garde, collectively know as the New York School.
- 1956 - Nuclear testing: Shot Redwing-Cherokee is successfully detonated at Bikini Atoll at the Pacific Proving Grounds in the Marshall Islands. With a yield of 3.8 megatons, it is the first aircraft deliverable hydrogen bomb tested by the United States.
- 1958 - United Kingdom Postmaster General Ernest Marples announces that from December, Subscriber Trunk Dialling will be introduced in the Bristol area.
- 1961 - American civil rights movement: Alabama Governor John Malcolm Patterson declares martial law in an attempt to restore order after race riots break out.
- 1972 - Michelangelo's Pietà, in St. Peter's Basilica in Rome, is damaged by a vandal.
- 1979 - White Night riots in San Francisco following the manslaughter conviction of Dan White for the assassinations of George Moscone and Harvey Milk.
- 1980 - Star Wars Episode V: The Empire Strikes Back is released into theaters.
- 1981 - Pierre Mauroy becomes Prime Minister of France.
- 1991 - Former Indian prime minister Rajiv Gandhi is assassinated by a female suicide bomber near Madras.
- 1996 - The MV Bukoba sinks in Tanzanian waters on Lake Victoria, killing nearly 1000.
- 1998 - At Thurston High School in Springfield, Oregon, Kipland Kinkel, suspended for bringing a gun to school, shoots a semi-automatic rifle into a room filled with students, killing 2 wounding 25 others after killing his parents at home.
- 1998 - In Miami, Florida, five abortion clinics are hit by a butyric acid attacker.
- 1998 - Soeharto, Indonesian dictator who had been ruling for 32 years, resigned.
- 2000 - A chartered British Aerospace Jetstream 31 crashes near Wilkes-Barre, Pennsylvania, killing 19.
- 2001 - French Taubira law which officially recognize the Atlantic slave trade and slavery as crimes against humanity.
- 2003 - An earthquake hits northern Algeria, killing more than 2,000 people.
- 2004 - Sherpa Pemba Dorjie climbs Mount Everest in 8 hours 10 minutes, breaking his rival Sherpa Lakpa Gelu's record from the previous year.
- 2004 - Stanislav Petrov is awarded the World Citizen Award for averting a potential World War III in 1983.
- 2005 - In Kiev, Ukraine, Greece wins the fiftieth Eurovision Song Contest with "My Number One" performed by Elena Paparizou.
- 2006 - The Republic of Montenegro holds a referendum proposing independence from the State Union of Serbia and Montenegro; Montenegrin people choose independence by the majority of 55%.
- 2006 - The Swedish ice hockey team Tre Kronor takes gold in the World Championship, becoming the first nation to hold both the World and Olympic titles separately in the same year.
- 2007 - One of the best-preserved clippers in existence, the Cutty Sark, while preserved in Greenwich, is severely damaged by fire.
Events (May 22nd) - 334 BC - The Greek army of Alexander the Great defeats Darius III of Persia in the Battle of the Granicus.
- 1176 - Murder attempt by the Hashshashin (Assassins) on Saladin near Aleppo.
- 1377 - Pope Gregory XI issues five papal bulls to denounce the doctrines of English theologian John Wycliffe.
- 1455 - Wars of the Roses: At the First Battle of St Albans, Richard, Duke of York, defeats and captures King Henry VI of England.
- 1762 - Sweden and Prussia sign the Treaty of Hamburg.
- 1807 - A grand jury indicts former Vice President of the United States Aaron Burr on a charge of treason.
- 1809 - Second and last Day of the Battle of Aspern-Essling (near Vienna), Napoleon was repelled by an enemy army for the first time.
- 1819 - The SS Savannah leaves port at Savannah, Georgia, United States, on a voyage to become the first steamship to cross the Atlantic Ocean. The ship arrived at Liverpool, England on June 20.
- 1840 - The transporting of British convicts to the New South Wales colony is abolished.
- 1842 - Farmers Lester Howe and Henry Wetsel discover Howe Caverns, when they stumble upon a large gaping hole in the ground.
- 1843 - Thousands of people and their cattle headed west via wagon train from Independence, Missouri to what would later become the Oregon Territory. It was part of the Great Migration. They followed what is now known as the Oregon Trail.
- 1844 - Persian Prophet The Báb announces His revelation, founding Bábism. He announced to the world of the coming of "He whom God shall make manifest." He is considered the forerunner of Bahá'u'lláh, the founder of the Bahá'í Faith.
- 1856 - Congressman Preston Brooks of South Carolina beats Senator Charles Sumner with a cane in the hall of the United States Senate for a speech Sumner had made attacking Southerners who sympathized with the pro-slavery violence in Kansas ("Bleeding Kansas").
- 1872 - Reconstruction: U.S. President Ulysses S. Grant signs the Amnesty Act of 1872 into law restoring full civil rights to all but about 500 Confederate sympathizers.
- 1906 - The 1906 Summer Olympics, not now recognized as part of the official Olympic Games, opens in Athens.
- 1906 - Wright brothers are granted U.S. patent number 821,393 for their "Flying-Machine".
- 1915 - Lassen Peak erupts with a powerful force, and is the only mountain to erupt other than Mount St. Helens in the continental US during the 20th century.
- 1915 - Five trains collide in the Quintinshill rail crash near Gretna Green, Scotland, killing 227 people and injuring 246; the accident is found to be the result of non-standard operating practices during a shift change at a busy junction.
- 1936 - Aer Lingus (Aer Loingeas) is founded by the Irish government as the national airline of the Republic of Ireland.
- 1939 - World War II: Germany and Italy sign the Pact of Steel.
- 1942 - Mexico enters World War II on the side of the Allies.
- 1942 - The Steel Workers Organizing Committee disbands, and a new trade union, the United Steelworkers, is formed.
- 1942 - World War II: Ted Williams of the Boston Red Sox enlists in the U.S. Navy Air Corps.
- 1947 - Cold War: In an effort to fight the spread of Communism, U.S. President Harry S. Truman signs an act into law that will later be called the Truman Doctrine. The act grants $400 million in military and economic aid to Turkey and Greece.
- 1960 - An earthquake measuring 9.5 on the Richter scale, now known as the Great Chilean Earthquake, hits southern Chile. It is the most powerful earthquake ever recorded.
- 1962 - Continental Airlines Flight 11 crashes after bombs explode.
- 1963 - Assassination attempt of Greek left-wing politician Gregoris Lambrakis, who will die five days afterwards.
- 1964 - U.S. President Lyndon B. Johnson announces the goals of his Great Society social reforms to bring an "end to poverty and racial injustice" in America.
- 1967 - The Innovation department store in the centre of Brussels, Belgium, burns down. It is the most devastating fire in Belgian history, which results in 323 dead and missing and 150 injured.
- 1968 - The nuclear-powered submarine the USS Scorpion sinks with 99 men aboard 400 miles southwest of the Azores.
- 1969 - Apollo 10's lunar module flies within 8.4 nautical miles (16 km) of the moon's surface.
- 1972 - Ceylon adopts a new constitution, changes its name to Sri Lanka, and joins the Commonwealth of Nations.
- 1981 - British serial killer Peter Sutcliffe, aka The Yorkshire Ripper, starts a life sentence.
- 1990 - North and South Yemen are unified to create the Republic of Yemen.
- 1990 - The Windows 3.0 operating system is released by Microsoft.
- 1992 - After 30 years, 66-year-old Johnny Carson hosts The Tonight Show for the last time.
- 1995 - Bangladesh Shahityacharcha Kendro established.
- 1997 - Kelly Flinn, US Air Force's first female bomber pilot certified for combat, accepts a general discharge in order to avoid a court martial.
- 1998 - Lewinsky scandal: A federal judge rules that United States Secret Service agents can be compelled to testify before a grand jury concerning the scandal, involving President Bill Clinton.
- 2002 - In Washington, DC, the remains of the missing Chandra Levy are found in Rock Creek Park.
- 2002 - American civil rights movement: A jury in Birmingham, Alabama, convicts former Ku Klux Klan member Bobby Frank Cherry of the 1963 murders of four girls in the bombing of the 16th Street Baptist Church.
- 2003 - In Fort Worth, Texas, Annika Sörenstam becomes the first woman to play the PGA Tour in 58 years.
- 2004 - Felipe, Prince of Asturias, of the Spanish Royal Family marries Letizia Ortiz Rocasolano.
- 2004 - The U.S. town of Hallam, Nebraska, is wiped out by a powerful F4 tornado that broke a width record at an astounding 2.5 miles wide. It also killed one local resident.
- 2006 - Results from the Montenegrin independence referendum, 2006 are announced. 55.4% of voters voted to become independent from the Serbia and Montenegro Union.
Events (May 23rd)- 1430 - Joan of Arc is captured by the Burgundians while leading an army to relieve Compiègne. (See Siege of Compiègne.)
- 1498 - Girolamo Savonarola is burned at the stake, in Florence, Italy, on the orders of Pope Alexander VI
- 1533 - The marriage of King Henry VIII to Catherine of Aragon is declared null and void.
- 1541 - Jacques Cartier leaves St-Malo, France on his third voyage.
- 1555 - Paul IV becomes Pope.
- 1568 - Netherlands declared independence from Spain.
- 1568 - Dutch rebels led by Louis of Nassau, brother of William I of Orange, defeat Jean de Ligne, Duke of Aremberg and his loyalist troops in the Battle of Heiligerlee, opening the Eighty Years' War.
- 1609 - Official ratification of the Second Charter of Virginia takes place.
- 1618 - The Second Defenestration of Prague precipitates the Thirty Years' War.
- 1701 - After being convicted of piracy and of murdering William Moore, Captain William Kidd is hanged in London.
- 1706 - Battle of Ramillies - the John Churchill, 1st Duke of Marlborough defeats a French army under Marshal Villeroi.
- 1788 - South Carolina becomes the 8th U.S. state to ratify the United States Constitution.
- 1805 - Napoleon Bonaparte is crowned King of Italy with the Iron Crown of Lombardy in the Cathedral of Milan.
- 1813 - South American independence leader Simón Bolívar enters Mérida, leading the invasion of Venezuela, and is proclaimed El Libertador ("The Liberator").
- 1844 - over the prior night the Persian Prophet the Báb announces his revelation, founding Bábísm. He announced to the world of the coming of "He whom God shall make manifest." He is considered the forerunner of Bahá'u'lláh, the founder of the Bahá'í Faith.
- 1846 - Mexican-American War: Mexico declares war on the United States.
- 1863 - Organization of the Seventh-day Adventist Church in Battle Creek, Michigan.
- 1863 - The Siege of Port Hudson starts.
- 1873 - The Canadian Parliament establishes the North West Mounted Police, the forerunner of the Royal Canadian Mounted Police.
- 1900 - American Civil War: Sergeant William Harvey Carney becomes the first African American to be awarded the Medal of Honor, for his heroism in the Assault on the Battery Wagner.
- 1907 - Unicameral Parliament of Finland gathered for its first plenary session.
- 1911 - Dedication ceremony for the New York Public Library.
- 1915 - World War I: Italy joins the Allies after they declare war on Austria-Hungary.
- 1923 - Launch of Belgium's SABENA airline.
- 1929 - The first talking cartoon of Mickey Mouse, The Karnival Kid, was released.
- 1933 - Seabiscuit, legendary American racehorse, is born
- 1934 - American bank robbers Bonnie and Clyde were ambushed by police and killed in Black Lake, Louisiana.
- 1934 - The Auto-Lite Strike culminated in the "Battle of Toledo," a five-day melee between 1,300 troops of the Ohio National Guard and 6,000 picketers.
- 1939 - The U.S. Navy submarine USS Squalus sinks off the coast of New Hampshire during a test dive, causing the death of 26 sailors. The remaining 32 crewmen and one passenger are rescued the following day.
- 1945 - World War II: Heinrich Himmler, the head of the SS, commits suicide while in Allied custody.
- 1945 - World War II: The Flensburg government under Reichspräsident Karl Dönitz was dissolved when its members were captured and arrested by British forces at Flensburg in Northern Germany.
- 1949 - The Federal Republic of Germany is established, and the Basic Law for the Federal Republic of Germany proclaimed.
- 1958 - Explorer I ceases transmission.
- 1960 - Prime Minister of Israel David Ben-Gurion announces that Nazi war criminal Adolf Eichmann has been captured.
- 1967 - Egypt closes the Straits of Tiran and blockades the port of Eilat at the northern end of the Gulf of Aqaba to Israeli shipping, laying the foundations for the Six Day War.
- 1969 - Rock band The Who release Tommy, the first rock opera.
- 1970 - An outbreak of fire occurs in the Britannia Bridge over the Menai Straits in north Wales contributing to its partial destruction and amounting to approximately £1,000,000 worth of fire damage.
- 1977 - Two terrorist actions unfold in The Netherlands: Several dozen hostages are taken onboard a train, and about 100 others (mostly children) are held at a Dutch school. The train siege lasts until June 11.
- 1985 - U.S. engineer Thomas Patrick Cavanagh is sentenced to life in prison for attempting to sell stealth bomber secrets to the Soviet Union.
- 1995 - Oklahoma City bombing: In Oklahoma City, Oklahoma, what remains of the Alfred P. Murrah Federal Building is imploded.
- 1997 - Mohammad Khatami is elected as President of Iran.
- 1998 - The Good Friday Agreement is accepted in a referendum, with a high margin of three-fourth 'yes' votes to Northern Ireland.
- 2002 - The "55 parties" clause of the Kyoto protocol is reached after its ratification by Iceland.
- 2003 - The euro exceeds its initial trading value as it hits $1.18 for the first time since its introduction in 1999.
- 2003 - 25-year-old Nepalese Sherpa, Pemba Dorjie Sherpa, makes the fastest-ever ascent of Mount Everest, in 12 hours 45 minutes. This is broken by his rival Sherpa Lakpa Gelu only three days later.
- 2004 - Part of Paris Charles De Gaulle International Airport Terminal 2E collapses, killing four people and injuring three others.
- 2007 - Parliament of Finland celebrated its 100th anniversary plenary session, with President Tarja Halonen and veterans in attendance.
Events (May 24th) - 1218 - The Fifth Crusade leaves Acre for Egypt.
- 1276 - Magnus Ladulås crowned King of Sweden in Uppsala Cathedral.
- 1487 - Imposter Lambert Simnel is crowned as "King Edward VI" at Dublin.
- 1595 - Nomenclator of Leiden University Library appears, the first printed catalog of an institutional library.
- 1621 - Protestant Union formally dissolved.
- 1626 - Peter Minuit buys Manhattan.
- 1689 - The English Parliament passes the Act of Toleration protecting Protestants (Roman Catholics are intentionally excluded).
- 1738 - John Wesley is converted, essentially launching the Methodist movement; the day is celebrated annually by Methodists as Aldersgate Day.
- 1798 - Irish Rebellion of 1798 led by the United Irishmen against British rule begins.
- 1822 - Battle of Pichincha: Antonio José de Sucre secures the independence of the Presidency of Quito.
- 1830 - Mary had a little lamb by Sarah Hale is published.
- 1830 - The first revenue trains in the United States begin service on the Baltimore and Ohio Rail Road between Baltimore and Ellicott's Mills.
- 1832 - The First Kingdom of Greece is declared in the London Conference.
- 1844 - Samuel F. B. Morse sent the message "What hath God wrought" (a Bible quotation, Numbers 23:23) from the Supreme Court room in Washington, D.C. to his assistant, Alfred Vail, in Baltimore, Maryland.
- 1846 - Mexican-American War: General Zachary Taylor captures Monterrey.
- 1856 - John Brown and his men murder five slavery supporters at Pottawatomie Creek, Kansas.
- 1861 - American Civil War: Union troops occupy Alexandria, Virginia.
- 1881 - Turkey cedes Thessaly and Arta back to Greece.
- 1883 - The Brooklyn Bridge in New York is opened to traffic after 14 years of construction.
- 1893 - The Niagara Falls Park and River Railway opens in Ontario.
- 1895 - Henry Irving becomes the first personage from the theatre to be knighted.
- 1899 - The first public parking garage in the United States is opened in Boston, Massachusetts.
- 1900 - Second Boer War: The United Kingdom annexes the Orange Free State.
- 1911 - The New York Public Library opened.
- 1915 - World War I: Italy declares war on Austria-Hungary.
- 1921 - The trial of Sacco and Vanzetti opens.
- 1929 - The Cocoanuts, the first film to star the Marx Brothers, opens.
- 1930 - Amy Johnson lands in Darwin, Northern Territory, becoming the first woman to fly from England to Australia (she left on May 5 for the 11,000 mile flight).
- 1935 - Crosley Field in Cincinnati, Ohio, hosts major-league baseball's first night game ever as the Cincinnati Reds beat the Philadelphia Phillies 2-1.
- 1940 - Igor Sikorsky performs the first successful single-rotor helicopter flight.
- 1941 - World War II: In the North Atlantic, the German Battleship BismarckHood killing all but three crewmen on what was the pride of the Royal Navy. sinks the HMS
- 1943 - Holocaust: Josef Mengele becomes chief medical officer in Auschwitz concentration camp.
- 1949 - The Soviet Union ends the 11-month Berlin Blockade.
- 1956 - The first Eurovision Song Contest is held in Lugano, Switzerland and is won by the host nation.
- 1956 - Conclusion of the Sixth Buddhist Council on Vesak Day, marking the 2,500 year anniversary after the Lord Buddha's Parinibbāna.
- 1958 - United Press International is formed through a merger of the United Press and the International News Service.
- 1961 - American civil rights movement: Freedom Riders are arrested in Jackson, Mississippi for "disturbing the peace" after disembarking from their bus.
- 1961 - Cyprus enters the Council of Europe.
- 1962 - Project Mercury: American astronaut Scott Carpenter orbits the Earth three times in the Aurora 7 space capsule.
- 1968 - Students set fire to the Paris bourse.
- 1968 - FLQ separatists bomb the U.S. consulate in Quebec City.
- 1970 - The drilling of the Kola Superdeep Borehole begins in the USSR
- 1973 - Earl Jellicoe resigns as Lord Privy Seal and Leader of the Lords.
- 1974 - After a nine-year run, The Dean Martin Show airs for the last time.
- 1975 - A group of 80 reporters and cameramen are the first Westerners allowed to leave Saigon in South Vietnam since it fell to communist forces on April 29.
- 1976 - London to Washington, DC Concorde service begins.
- 1980 - The International Court of Justice calls for the release of United States embassy hostages in Tehran. The hostages would not be freed until the following January.
- 1981 - First International Women's Day for Disarmament.
- 1982 - Liberation of Khorramshahr, Iranians recapture of the port city of Khorramshahr from the Iraqis during Iran-Iraq War
- 1988 - Section 28 is passed as law by Parliament in the United Kingdom.
- 1989 - Sonia Sutcliffe, wife of the Yorkshire Ripper, is awarded a six-figure sum in damages after winning a libel action against Private Eye.
- 1990 - A car carrying American Earth First! activists Judi Bari and Darryl Cherney explodes in Oakland, California, critically injuring both.
- 1991 - Israel conducts Operation Solomon, evacuating Ethiopian Jews to Israel.
- 1992 - The last Thai dictator, General Suchinda Kraprayoon, resigns following pro-democracy protests.
- 1993 - Eritrea gains its independence from Ethiopia.
- 1993 - Microsoft unveils Windows NT.
- 1994 - Four men convicted of bombing New York's World Trade Center in 1993 are each sentenced to 240 years in prison.
- 1999 - Venezuela entered the Antarctic Treaty System.
- 2000 - Israeli troops withdraw from southern Lebanon after 22 years of occupation.
- 2001 - Mountain climbing: 15-year-old Sherpa Temba Tsheri becomes the youngest person to climb to the top of Mount Everest.
- 2001 - The Versailles wedding hall collapse in Jerusalem, Israel, kills 23 and injures over 200 in Israel's worst-ever civil disaster.
- 2001 - The Democrats gain control of the U.S. Senate for the first time since 1994 when Senator James Jeffords of Vermont abandons the Republican Party and declares himself an independent.
- 2002 - Russia and the United States sign the Moscow Treaty.
Events (May 25th) - 1085 - Alfonso VI of Castile takes Toledo back from the Moors.
- 1420 - Henry the Navigator is appointed governor of the Order of Christ.
- 1521 - The Diet of Worms ends when Charles V, Holy Roman Emperor, issues the Edict of Worms, declaring Martin Luther an outlaw.
- 1659 - Richard Cromwell resigns as Lord Protector of England following the restoration of the Long Parliament, beginning a second brief period of the republican government called the Commonwealth.
- 1787 - In Philadelphia, Pennsylvania, delegates convene a Constitutional Convention to write a new Constitution for the United States. George Washington presides.
- 1810 - In the May Revolution, citizens of Buenos Aires expel the Viceroy during the Semana de Mayo.
- 1865 - In Mobile, Alabama, 300 are killed when an ordnance depot explodes.
- 1895 - Playwright, poet and novelist Oscar Wilde is convicted of "committing acts of gross indecency with other male persons" and sentenced to serve two years in prison.
- 1895 - The Republic of Formosa is formed, with Tang Ching-sung as the president.
- 1901 - River Plate was founded to become one of the most succesful teams in Argentina.
- 1914 - The United Kingdom's House of Commons passes Home Rule Act for devolution in Ireland.
- 1925 - Scopes Trial: John T. Scopes is indicted for teaching Darwin's theory of evolution.
- 1926 - Sholom Schwartzbard assassinates Symon Petliura, the head of the Paris-based government-in-exile of Ukrainian People's Republic.
- 1935 - Babe Ruth hits his 714th and last home run at Forbes Field in Pittsburgh, Pennsylvania, setting a baseball record that will stand for 39 years.
- 1936 - The Remington Rand strike, led by the American Federation of Labor, begins.
- 1938 - Spanish Civil War: Bombing of Alicante, 313 deaths.
- 1940 - World War II: The Battle of Dunkirk begins.
- 1946 - The parliament of Transjordan makes Abdullah I of Jordan their king.
- 1953 - Nuclear testing: At the Nevada Test Site, the United States conducts its first and only nuclear artillery test.
- 1955 - In the United States, a night time F5 tornado strikes the small city of Udall, Kansas, killing 80 and injuring 273. It was the deadliest tornado to ever occur in the state and the 23rd deadliest in the U.S.
- 1961 - Apollo program: U.S. president John F. Kennedy announces before a special joint session of Congress his goal to initiate a project to put a "man on the moon" before the end of the decade.
- 1961 - King Hussein of Jordan marries Princess Muna al-Hussein (Antoinette Gardiner).
- 1963 - In Addis Ababa, Ethiopia, the Organisation of African Unity is established.
- 1966 - Explorer program: Explorer 32 launches.
- 1966 - The first prominent DaZiBao during the Cultural Revolution in China was posted at Peking University.
- 1967 - Celtic F.C. become the first British and Non-Latin to win the European Champions' Cup in the Lisbon Lions 2-1 victory over Inter Milan in Lisbon, Portugal.
- 1977 - George Lucas' film Star Wars, is released, and becomes an instant hit.
- 1977 - Liverpool F.C. win their first European Champions' Cup, defeating Borussia Moenchengladbach 3-1 in the Stadio Olimpico, Rome.
- 1979 - American Airlines Flight 191: In Chicago, a DC-10 crashes during takeoff at O'Hare International Airport killing 271 on board and two people on the ground.
- 1979 - Florida executes John Spenkelink, the first non-voluntary execution in the United States in more than 10 years.
- 1981 - In Riyadh, the Gulf Cooperation Council is created between Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates.
- 1982 - HMS Coventry is sunk during the Falklands War.
- 1985 - Bangladesh is hit by a tropical cyclone and storm surge, which kills approximately 10,000 people.
- 1986 - Hands Across America, a benefit event, takes place.
- 1992 - The first episode of Shortland Street screens.
- 1995 - The Bosnian Serb Army kills 72 youngsters in the Bosnian city of Tuzla.
- 1997 - A military coup in Sierra Leone replaces President Ahmad Tejan Kabbah with Major Johnny Paul Koromah.
- 1999 - The United States House of Representatives released the Cox Report which detailed the People's Republic of China's nuclear espionage against the U.S. over the prior two decades.
- 2000 - Liberation Day of Lebanon. Israel withdraws its army from most of the Lebanese territory after 22 years of its first invasion in 1978.
- 2001 - 32-year-old Erik Weihenmayer, of Boulder, Colorado, becomes the first blind person to reach the summit of Mount Everest.
- 2001 - 64-year-old Sherman Bull, of New Canaan, Connecticut, becomes the oldest person to reach the summit of Mount Everest.
- 2002 - China Airlines Flight 611: A Boeing 747-200 breaks apart in mid-air and plunges into the Taiwan Strait killing 225 people.
- 2002 - A train crash in Tenga, Mozambique kills 197 people.
- 2003 - Néstor Kirchner becomes President of Argentina after defeating Carlos Menem. He is the first elected President since the economic crisis.
- 2005- Liverpool FC win the European Cup for the fifth time.
- 2007 - the Ostankino Tower in Moscow, Russia catches fire for the second time.
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