21 October

1096 – People's Crusade: The Turkish army annihilates the People's Army of the West.
1097 – First Crusade: Crusaders led by Godfrey of Bouillon, Bohemund of Taranto, and Raymond IV of Toulouse, begin the Siege of Antioch.
1209 – Otto IV is crowned emperor of the Holy Roman Empire by Pope Innocent III.
1392 – Nanboku-chō: Emperor Go-Kameyama abdicates in favor of rival claimant Go-Komatsu.
1512 – Martin Luther joins the theological faculty of the University of Wittenberg.
1520 – Ferdinand Magellan discovers a strait now known as Strait of Magellan.
1520 – João Álvares Fagundes discovers the islands of Saint-Pierre and Miquelon, bestowing them their original name of "Islands of the 11,000 Virgins".
1600 – Tokugawa Ieyasu defeats the leaders of rival Japanese clans in the Battle of Sekigahara, which marks the beginning of the Tokugawa shogunate that in effect rules Japan until the mid-nineteenth century.
1774 – First display of the word "Liberty" on a flag, raised by colonists in Taunton, Massachusetts in defiance of British rule in Colonial America.
1797 – In Boston Harbor, the 44-gun United States Navy frigate USS Constitution is launched.
1805 – Napoleonic Wars: Battle of Trafalgar: A British fleet led by Vice Admiral Lord Nelson defeats a combined French and Spanish fleet off the coast of Spain under Admiral Villeneuve. It signals almost the end of French maritime power and leaves Britain's navy unchallenged until the 20th century.
1816 – The Penang Free School is founded in George Town, Penang, Malaysia, by the Rev Hutchings. It is the oldest English-language school in Southeast Asia.
1824 – Joseph Aspdin patents Portland cement.
1854 – Florence Nightingale and a staff of 38 nurses are sent to the Crimean War.
1861 – American Civil War: Battle of Ball's Bluff – Union forces under Colonel Edward Baker are defeated by Confederate troops in the second major battle of the war. Baker, a close friend of Abraham Lincoln, is killed in the fighting.
1867 – Manifest Destiny: Medicine Lodge Treaty – Near Medicine Lodge, Kansas a landmark treaty is signed by southern Great Plains Indian leaders. The treaty requires Native American Plains tribes to relocate a reservation in western Oklahoma.
1892 – Opening ceremonies for the World's Columbian Exposition are held in Chicago, though because construction was behind schedule, the exposition did not open until May 1, 1893.
1895 – The Republic of Formosa collapses as Japanese forces invade.
1902 – In the United States, a five month strike by United Mine Workers ends.
1912 – During the First Balkan War, Kardzhali is liberated by Bulgarian forces
1921 – President Warren G. Harding delivers the first speech by a sitting President against lynching in the deep south.
1921 – George Melford's silent film, The Sheik, starring Rudolph Valentino, premiers.
1931 – The Sakurakai, a secret society in the Imperial Japanese Army, launches an abortive coup d'état attempt.
1944 – World War II: The first kamikaze attack: A Japanese plane carrying a 200-kilogram (440 lb) bomb attacks HMAS Australia off Leyte Island, as the Battle of Leyte Gulf began.
1944 – World War II: Battle of Aachen: The city of Aachen falls to American forces after three weeks of fighting, making it the first German city to fall to the Allies.
1945 – Women's suffrage: Women are allowed to vote in France for the first time.
1950 – Korean War: heavy fighting begins between British and Australian forces from the 27th British Commonwealth Brigade and the North Korean 239th Regiment during the Battle of Yongju.
1956 – Kenyan rebel leader Dedan Kimathi is captured by the British Army, signalling the ultimate defeat of the Mau Mau Uprising, and essentially ending the British military campaign.
1959 – In New York City, the Solomon R. Guggenheim Museum, designed by Frank Lloyd Wright, opens to the public.
1959 – President Dwight D. Eisenhower signs an executive order transferring Wernher von Braun and other German scientists from the United States Army to NASA.
1965 – Comet Ikeya-Seki approaches perihelion, passing 450,000 kilometers from the sun.
1966 – Aberfan disaster: A slag heap collapses on the village of Aberfan in Wales, killing 144 people, mostly schoolchildren.
1967 – Vietnam War: More than 100,000 war protesters gather in Washington, D.C.. A peaceful rally at the Lincoln Memorial is followed by a march to The Pentagon and clashes with soldiers and United States Marshals protecting the facility. Similar demonstrations occurred simultaneously in Japan and Western Europe.
1969 – A coup d'état in Somalia brings Siad Barre to power.
1971 – A gas explosion kills 22 people at a shopping centre in Clarkston, East Renfrewshire, near Glasgow, Scotland.
1973 – John Paul Getty III's ear is cut off by his kidnappers and sent to a newspaper in Rome; it doesn't arrive until November 8.
1973 – Fred Dryer of the then Los Angeles Rams becomes the first player in NFL history to score two safeties in the same game.
1977 – The European Patent Institute is founded.
1978 – Australian civilian pilot Frederick Valentich vanishes in a Cessna 182 over the Bass Strait south of Melbourne, after reporting contact with an unidentified aircraft.
1979 – Moshe Dayan resigns from the Israeli government because of strong disagreements with Prime Minister Menachem Begin over policy towards the Arabs.
1983 – The metre is defined at the seventeenth General Conference on Weights and Measures as the distance light travels in a vacuum in 1/299,792,458 of a second.
1986 – In Lebanon, pro-Iranian kidnappers claim to have abducted American writer Edward Tracy (he is released in August 1991).
1987 – Jaffna hospital massacre is carried out by Indian Peace Keeping Force in Sri Lanka killing 70 ethnic Tamil patients, doctors and nurses.
1994 – North Korea nuclear weapons program: North Korea and the United States sign an agreement that requires North Korea to stop its nuclear weapons program and agree to inspections.
1994 – In Seoul, 32 people are killed when the Seongsu Bridge collapses.
2003 – Images of the dwarf planet Eris are taken and subsequently used in documenting its discovery by the team of Michael E. Brown, Chad Trujillo, and David L. Rabinowitz.

Holidays and observances

Apple Day (United Kingdom)
Christian Feast Day:
Hilarion
John of Bridlington
Leticia
Ursula
International Day of the Nacho (Mexico and USA)
National Nurses' Day (Thailand)
Overseas Chinese Day (Republic of China)
Trafalgar Day (the British Empire in the 19th and early 20th century)