| 20 September 1378 | France, Italy [administration] | Dissident cardinals, encouraged by King Charles V of France, elect Robert of Geneva as Pope Clement VII. This means that there are two current Popes. |
| 20 September 1410 | Holy Roman Empire, Germany, Hungary [political events] | Following the death of the Holy Roman Emperor Rupert III of Wittelsbach, King Sigismund of Hungary is elected his successor. |
| 20 September 1854 | Russian Empire, UK, France [Crimean War (1854–56)] | British and French troops are victorious over Russian forces at the Battle of the Alma in the Crimean War. |
| 20 September 1863 | Germany [births and deaths] | Jacob Grimm, German author (with his brother Wilhelm) of Grimm's Fairy Tales (1812), dies in Berlin, Germany (78). |
| 20 September 1902 | [births and deaths] | (Florence Margaret) ‘Stevie’ Smith, English poet, born in Hull, Yorkshire, England (–1971). |
| 20 September 1951 | USA [space exploration] | The US Air Force makes the first successful recovery of animals from a rocket flight when a monkey and 11 mice are recovered from a flight to an altitude of 72,000 m/236,000 ft. |
| 20 September 1967 | Nigeria, Dahomey [decolonization] | The mid-west of Nigeria proclaims itself independent as Dahomey (now Benin). |
| 20 September 1979 | Central African Empire [law and government] | The former president of the Central African Empire (now Central African Republic) David Dacko overthrows his uncle, Emperor Jean-Bédel Bokassa, and the country reverts to republic status. |
| 20 September 1984 | [television] | The Cosby Show, a situation comedy about a middle-class black family, begins on US television. It is the top-rated US television show during the 1980s. |
| 20 September 1992 | France [treaties] | A French referendum produces a vote narrowly (51.04%) in favour of ratification of the Maastricht Treaty on European, as agreed in the Netherlands on 10 December 1991. |
| 20 September 1997 | UK [popular music] | The English pop star Elton John releases the single ‘Candle in the Wind ‘97’ as a tribute to Diana, Princess of Wales. It goes immediately to number one and becomes the best-selling single of all time. |
| 20 September 2005 | Austria [births and deaths] | Simon Wiesenthal, Austrian Holocaust survivor and veteran hunter of Nazi war criminals after World War II, dies in Vienna, Austria (96). |
