| 99241 | September 1 | Event | 1920 – The Fountain of Time opens as a tribute to the 100 years of peace between the United States and Great Britain following the Treaty of Ghent. |
| 99242 | September 1 | Event | 1923 – The Great Kantō earthquake devastates Tokyo and Yokohama, killing about 105,000 people. |
| 99243 | September 1 | Event | 1928 – Ahmet Zogu declares Albania to be a monarchy and proclaims himself king. |
| 99244 | September 1 | Event | 1934 – SMJK Sam Tet is founded by Father Fourgs from the St. Michael Church, Ipoh, Perak, Malaysia. |
| 99245 | September 1 | Event | 1939 – World War II: Nazi Germany and Slovakia invade Poland, beginning the European phase of World War II. |
| 99246 | September 1 | Event | 1939 – General George C. Marshall becomes Chief of Staff of the United States Army. |
| 99247 | September 1 | Event | 1939 – The Wound Badge for Wehrmacht, SS, Kriegsmarine, and Luftwaffe soldiers is instituted. The final version of the Iron Cross is also instituted on this date. |
| 99248 | September 1 | Event | 1939 – Switzerland mobilizes its forces and the Swiss Parliament elects Henri Guisan to head the Swiss Army (an event that can happen only during war or mobilization). |
| 99249 | September 1 | Event | 1939 – Adolf Hitler signs an order to begin the systematic euthanasia of mentally ill and disabled people. |
| 99250 | September 1 | Event | 1951 – The United States, Australia and New Zealand sign a mutual defense pact, called the ANZUS Treaty. |
| 99251 | September 1 | Event | 1951 – United Nations Security Council Resolution 95 relating to Arab-Israeli conflict is adopted. |
| 99252 | September 1 | Event | 1952 – The Old Man and the Sea, the Pulitzer Prize-winning novel by Ernest Hemingway, is first published. |
| 99253 | September 1 | Event | 1958 – Iceland expands its fishing zone, putting it into conflict with the United Kingdom, beginning the Cod Wars. |
| 99254 | September 1 | Event | 1961 – The Eritrean War of Independence officially begins with the shooting of the Ethiopian police by Hamid Idris Awate. |
| 99255 | September 1 | Event | 1961 – The first conference of the Non Aligned Countries is held in Belgrade. |
| 99256 | September 1 | Event | 1967 – The Khmer–Chinese Friendship Association is banned in Cambodia. |
| 99257 | September 1 | Event | 1969 – A coup in Libya brings Muammar Gaddafi to power. |
| 99258 | September 1 | Event | 1969 – Trần Thiện Khiêm becomes Prime Minister of South Vietnam under President Nguyễn Văn Thiệu. |
| 99259 | September 1 | Event | 1970 – Attempted assassination of King Hussein of Jordan by Palestinian guerrillas, who attack his motorcade. |
| 99260 | September 1 | Event | 1972 – In Reykjavík, Iceland, American Bobby Fischer beats Russian Boris Spassky to become the world chess champion. |
| 99261 | September 1 | Event | 1974 – The SR-71 Blackbird sets (and holds) the record for flying from New York to London in the time of 1 hour, 54 minutes and 56.4 seconds at a speed of 1,435.587 miles per hour (2,310.353 km/h). |
| 99262 | September 1 | Event | 1979 – The American space probe Pioneer 11 becomes the first spacecraft to visit Saturn when it passes the planet at a distance of 21,000 kilometres (13,000 mi). |
| 99263 | September 1 | Event | 1980 – Terry Fox's Marathon of Hope ends near Thunder Bay, Ontario. |
| 99264 | September 1 | Event | 1980 – Major General Chun Doo-hwan becomes President of South Korea, following the resignation of Choi Kyu-hah. |
| 99265 | September 1 | Event | 1981 – A coup d'état in the Central African Republic overthrows President David Dacko. |
| 99266 | September 1 | Event | 1982 – The United States Air Force Space Command is founded. |
| 99267 | September 1 | Event | 1983 – Cold War: Korean Air Lines Flight 007 is shot down by a Soviet Union jet fighter when the commercial aircraft enters Soviet airspace. All 269 on board die, including Congressman Lawrence McDonald. |
| 99268 | September 1 | Event | 1985 – A joint American–French expedition locates the wreckage of the RMS Titanic. |
| 99269 | September 1 | Event | 1991 – Uzbekistan declares independence from the Soviet Union. |
| 99270 | September 1 | Event | 1997 – The death of Diana, Princess of Wales, is announced by Buckingham Palace. |