| 17 September 14 | Roman Empire [political events] | Tiberius formally succeeds his adoptive father Augustus as Roman emperor. |
| 17 September 1176 | Byzantine Empire, Seljuk Sultanate of Rum [wars] | The Byzantine emperor Manuel I Comnenus invades the sultanate of Rum but his army is trapped and destroyed by Sultan Kilij Arslan II at Myriocephalum. |
| 17 September 1179 | Germany [births and deaths] | Hildegard von Bingen, German Benedictine abbess, philosopher, mystic, and musician, dies in Rupertsberg, near Bingen, Germany (c. 81). |
| 17 September 1312 | Castile, León, Spain [administration] | King Ferdinand IV of Castile and León dies. He is succeeded by his infant son, Alfonso XI. In the chaos caused by Alfonso's minority, civil war breaks out. |
| 17 September 1577 | France [French Wars of Religion (1562–80)] | By the Edict of Poitiers, King Henry III of France proclaims the Peace of Bergerac, ending the Sixth War of Religion. The Huguenots (French Protestants), negotiating from a position of weakness, are required to relinquish some concessions granted in the Peace of Monsieur of 6 May 1576: most importantly, their freedom of worship is now restricted to towns legitimately held heretofore. |
| 17 September 1631 | Sweden, Saxony, Germany, Holy Roman Empire [Thirty Years War (1618–48)] | King Gustavus II Adolphus of Sweden, supported by the Saxons, defeats the imperialist forces of Count Johan Tserclaus von Tilly at the Battle of Breitenfeld, near Leipzig, Sweden. Tilly's forces are shattered, and his defeat means that the Edict of Restitution of March 1629 cannot be enforced. |
| 17 September 1665 | Spain [administration] | King Philip IV of Spain dies and is succeeded by his underage son Charles II. A regency is established under Philip's widow Mariana. |
| 17 September 1678 | Spanish Netherlands, France, Spain [treaties] | The second Peace Treaty of Nijmegen is signed by the French and the Spanish. By its terms, Spain cedes Franche-Comté and exchanges some of her fortresses in the Spanish Netherlands with France. These include St Omer, Aire, Ypres, Valenciennes, Cambrai, and Mauberge. |
| 17 September 1730 | Ottoman Empire [political events] | Sultan Ahmed III of the Ottoman Empire resigns the throne to his nephew Mahmud I, a prisoner in the Seraglio since his father's own abdication in 1703, following the bloody uprising led by Patrona Halil and precipitated by high taxes, unemployment, and Ottoman defeats by Persia. |
| 17 September 1848 | Austrian Empire [political events] | Count Josip Jellacic leads a Croat invasion of Hungary, disputing Magyar domination of the Habsburg monarchy's Slav peoples. |
| 17 September 1862 | USA, Confederate States of America [American Civil War (1861–65)] | In the Battle of Antietam, Maryland, (Sharpsburg, in Confederate parlance), the Union army foils a Confederate advance on Washington, DC. Some 23,000 soldiers fall on this, the war's costliest day of fighting. President Abraham Lincoln uses the Union ‘victory’ as a pretext for issuing the Emancipation Proclamation five days later. |
| 17 September 1920 | USA [American football] | A new professional American football league, the American Professional Football Association, the forerunner of the National Football League, is formed at Canton, Ohio. It comprises 10 teams (soon extended to 14). |
| 17 September 1939 | USSR, Poland [World War II (1939–45)] | Red Army troops from the USSR invade Poland from the east, to effect the secretly agreed partition of Poland with Germany. |
| 17–28 September 1944 | Netherlands, USA, UK [World War II (1939–45)] | In Operation Market Garden in the Netherlands, US airborne troops land at Eindhoven and Nijmegen to seize bridges over the rivers Maas, Waal, and Rhine (Market), while British troops land at Arnhem on the Rhine to open a route to the Ruhr region in Germany (Garden). The landing at Arnhem is a disaster. |
| 17 September 1973 | UK, Ireland [law and government] | The British prime minister Edward Heath meets Prime Minister Liam Cosgrave of the Republic of Ireland at an airfield near Dublin for talks on Northern Ireland. It is the first official visit to the republic by a British prime minister. |
| 17 September 1982 | West Germany [political events] | The West German Social Democrat–Free Democrat government collapses following the withdrawal of Free Democrat ministers. On October 1, a new Christian Democrat–Free Democrat government is formed under Christian Democrat Leader Helmut Kohl. |
| 17 September 2007 | [business and economics] | A €500 million fine imposed by the European Commission in 2004 on the giant computer software company Microsoft for alleged anti-competitive practices is upheld in a ruling by the European Union's Court of First Instance. |
