27 May

927 – Battle of the Bosnian Highlands: the Croatian army, led by King Tomislav, defeats the Bulgarian Army.
1120 – Richard III of Capua is anointed as Prince two weeks before his untimely death.
1153 – Malcolm IV becomes King of Scotland.
1703 – Tsar Peter the Great founds the city of Saint Petersburg.
1798 – The Battle of Oulart Hill takes place in Wexford, Ireland.
1799 – War of the Second Coalition: Austrian forces defeats the French at Winterthur, Switzerland, securing control of the northeastern Swiss Plateau because of the town's location at the junction of seven cross-roads.
1812 – Bolivian War of Independence: In Bolivia, the Battle of La Coronilla, in which the women from Cochabamba fight against the Spanish army.
1813 – War of 1812: In Canada, American forces capture Fort George.
1849 – The Great Hall of Euston station in London is opened.
1860 – Giuseppe Garibaldi begins his attack on Palermo, Sicily, as part of the Italian Unification.
1863 – American Civil War: First Assault on the Confederate works at the Siege of Port Hudson.
1883 – Alexander III is crowned Tsar of Russia.
1896 – The F4-strength St. Louis-East St. Louis Tornado hits in St. Louis, Missouri and East Saint Louis, Illinois, killing at least 255 people and causing $2.9 billion in damage (1997 USD).
1905 – Russo-Japanese War: The Battle of Tsushima begins.
1907 – Bubonic plague breaks out in San Francisco, California.
1919 – The NC-4 aircraft arrives in Lisbon after completing the first transatlantic flight.
1927 – The Ford Motor Company ceases manufacture of the Ford Model T and begins to retool plants to make the Ford Model A.
1930 – The 1,046 feet (319 m) Chrysler Building in New York City, the tallest man-made structure at the time, opens to the public.
1933 – New Deal: The U.S. Federal Securities Act is signed into law requiring the registration of securities with the Federal Trade Commission.
1933 – The Walt Disney Company releases the cartoon Three Little Pigs, with its hit song "Who's Afraid of the Big Bad Wolf?"
1933 – The Century of Progress World's Fair opens in Chicago, Illinois.
1935 – New Deal: The Supreme Court of the United States declares the National Industrial Recovery Act to be unconstitutional in A.L.A. Schechter Poultry Corp. v. United States, (295 U.S. 495).
1937 – In California, the Golden Gate Bridge opens to pedestrian traffic, creating a vital link between San Francisco and Marin County, California.
1940 – World War II: In the Le Paradis massacre, 99 soldiers from a Royal Norfolk Regiment unit are shot after surrendering to German troops. Two survive.
1941 – World War II: U.S. President Franklin D. Roosevelt proclaims an "unlimited national emergency".
1941 – World War II: The German battleship Bismarck is sunk in the North Atlantic killing almost 2,100 men.
1942 – World War II: In Operation Anthropoid, Reinhard Heydrich is assassinated in Prague.
1957 – Toronto's CHUM-AM, (1050 kHz) becomes Canada's first radio station to broadcast only top 40 Rock n' Roll music format.
1958 – The F-4 Phantom II makes its first flight.
1960 – In Turkey, a military coup removes President Celal Bayar and the rest of the democratic government from office.
1962 – The Centralia, Pennsylvania mine fire starts.
1965 – Vietnam War: American warships begin the first bombardment of National Liberation Front targets within South Vietnam.
1967 – Australians vote in favor of a constitutional referendum granting the Australian government the power to make laws to benefit Indigenous Australians and to count them in the national census.
1967 – The U.S. Navy aircraft carrier USS John F. Kennedy is launched by Jacqueline Kennedy and her daughter Caroline.
1968 – The meeting of the Union Nationale des Étudiants de France (National Union of the Students of France) takes place. 30,000 to 50,000 people gather in the Stade Sebastien Charlety.
1971 – The Dahlerau train disaster, the worst railway accident in West Germany, kills 46 people and injures 25 near Wuppertal.
1975 – Dibbles Bridge Coach Crash near Grassington, North Yorkshire, England kills 33 – the highest ever death toll in a road accident in the United Kingdom.
1980 – The Gwangju Massacre: Airborne and army troops of South Korea retake the city of Gwangju from civil militias, killing at least 207 and possibly many more.
1986 – the game credited as setting the template for role-playing video games, Dragon Quest is released in Japan.
1995 – In Culpeper, Virginia, actor Christopher Reeve is paralyzed from the neck down after falling from his horse in a riding competition.
1996 – First Chechnya War: Russian President Boris Yeltsin meets with Chechnyan rebels for the first time and negotiates a cease-fire.
1997 – The unusual 1997 Central Texas tornado outbreak Jarrell, Texas
1997 – The U.S. Supreme Court rules that Paula Jones can pursue her sexual harassment lawsuit against President Bill Clinton while he is in office.
1998 – Oklahoma City bombing: Michael Fortier is sentenced to 12 years in prison and fined $200,000 for failing to warn authorities about the terrorist plot.
1999 – The International Criminal Tribunal for the former Yugoslavia in The Hague, Netherlands indicts Slobodan Milošević and four others for war crimes and crimes against humanity committed in Kosovo.
2001 – Members of Islamist separatist group Abu Sayyaf seize twenty hostages from an upscale island resort on Palawan in the Philippines; the hostage crisis would not be resolved until June 2002.
2005 – Australian Schapelle Corby is sentenced to 20 years imprisonment in Kerobokan Prison for drug smuggling by a court in Indonesia.
2005 – The first year of the Tunisian American Day, which became a yearly event
2006 – The May 2006 Java earthquake strikes at 5:53:58 am local time (22:53:58 UTC May 26) devastating Bantul and the city of Yogyakarta killing over 6,600 people.

Holidays and observances

Armed Forces Day (Nicaragua)
Children's Day (Nigeria)
Christian Feast Day:
Augustine of Canterbury
Bruno of Würzburg
Eutropius of Orange
Hildebert
Julius the Veteran
May 27 (Eastern Orthodox liturgics)
Mother's Day or Día de la Madre (Bolivia)
Slavery Abolition Day (Guadeloupe, Saint Barthélemy, Saint Martin)