| 21 October 1096 | Seljuk Sultanate of Rum [Crusades (1095–1272)] | Kilij Arslan, Seljuk sultan of Rum, destroys the army of the ‘People's Crusade’ at Civetot, shortly after it has crossed into Anatolia. |
| 21 October 1328 | China [births and deaths] | Hongwu or Hung-wu, Chinese emperor 1368–98, founder of the Ming dynasty, born in Hao-chou, China (–1398). |
| 21 October 1422 | France, England [administration] | In accordance with the 1420 Treaty of Troyes, King Henry VI of England succeeds to the French throne following the death of King Charles VI of France. |
| 21 October 1496 | Holy Roman Empire, Spain, France [political events] | Philip (‘the Handsome’), Duke of Burgundy and son of Maximilian I the Holy Roman Emperor, marries the Infanta Joanna (‘the Mad’), daughter of King Ferdinand V and Queen Isabella I, an event of great importance as it leads to the union of their families' realms. |
| 21 October–28 November 1520 | Spain, South America [exploration] | The Spanish expedition under the Portuguese navigator Ferdinand Magellan negotiates the strait which now bears his name, between the South American continent and the island of Tierra del Fuego. Three ships reach the Pacific Ocean and continue northwest, the fourth having turned back. |
| 21 October 1559 | Scotland [political events] | The Scottish Protestant Lords of the Congregation, led by James Hamilton, Earl of Arran, Duke of Châtelherault, and heir presumptive, depose the Scottish regent Mary of Guise in Edinburgh; she has allowed French reinforcements to fortify Leith. |
| 21 October 1639 | Spain, United Netherlands [Spanish–Dutch War (1621–48)] | The Spanish fleet under Antonio de Aquendo, bringing reinforcements to the Spanish army in Flanders, is destroyed by the Dutch under Admiral Maarten van Tromp at the Battle of the Downs. The battle is fought in English territorial waters and has the effect of cutting another means of communication between Madrid and the Spanish Netherlands. |
| 21 October 1652 | France [Fronde (1648–52)] | King Louis XIV of France returns to Paris, France, in triumph, re-establishing the government and exiling leading Frondeurs. |
| 21 October 1772 | England [births and deaths] | Samuel Taylor Coleridge, English Romantic poet, literary critic, and philosopher, born in Ottery St Mary, Devon, England (–1834). |
| 21 October 1805 | Spain [births and deaths] | Horatio Nelson, British naval commander who won decisive battles against France in the Revolutionary and Napoleonic Wars, is killed at sea off Cape Trafalgar, Spain (46). |
| 21 October 1805 | UK, France, Spain, Italy [Napoleonic Wars (1803–15)] | A Royal Navy fleet commanded by the English admiral Horatio Nelson defeats the combined Franco-Spanish fleet under Vice Admiral Pierre Villeneuve in the Battle of Trafalgar. Nelson is mortally wounded in the action, but the battle confirms Britain's naval superiority and removes any possibility of a French invasion of Britain. |
| 21 October 1847 | Switzerland [wars] | Civil war begins in Switzerland, following the Catholic cantons' refusal on 20 July to dissolve their armed league, the Sonderbund, in the face of a liberal, anticlerical majority in the diet. |
| 21 October 1879 | USA [technology] | US inventor Thomas Alva Edison demonstrates his carbon-filament incandescent lamp light. He lights his Menlo Park power station with 30 lamps that burn for two days; later filaments burn for several hundred hours. Each light can be turned on or off separately in the first demonstration of parallel circuit. |
| 21 October 1904 | Russian Empire, United Kingdom [Russo–Japanese War (1904–05)] | The Russian Baltic fleet, bound for the Far East via the Cape of Good Hope, fires on British trawlers in the Dogger Bank area of the North Sea, believing them to be Japanese torpedo boats. One vessel sinks, provoking a wave of indignation in Britain. |
| 21 October 1918 | Czechoslovakia [political events] | Czechoslovakia is proclaimed an independent republic in the Czech city of Prague. |
| 21 October 1959 | USA [museums and galleries] | The Solomon Guggenheim Museum, a modern art museum designed by US architect Frank Lloyd Wright, opens in New York City. |
| 21–22 October 1973 | USSR, USA, Egypt, Israel [diplomacy] | The US secretary of state Henry Kissinger and the general secretary of the Soviet Communist Party Leonid Brezhnev meeting in Moscow, agree a plan to stop the Yom Kippur War in the Middle East. Egypt and Israel accept a United Nations (UN) ceasefire on 22 October, but fighting continues. |
| 21 October 1993 | Burundi [political events] | President Melchior Ndadaye (Burundi's first Hutu president) and other senior ministers are killed during an attempted coup by the Tutsi-dominated army. |
| 21 October 1994 | USA, North Korea [political events] | The USA reaches an agreement with North Korea over its nuclear programme; North Korea agrees to submit to regular inspections, while the USA agrees to finance the modernization of North Korea's domestic nuclear industry and give it diplomatic recognition. |
