- 1630 - The city of Boston, Massachusetts, is founded.
- 1787 - The United States Constitution is signed in Philadelphia, Pennsylvania.
- 1862 - American Civil War: George B. McClellan halts the northward drive of Robert E. Lee's Confederate army in the single-day Battle of Antietam, the bloodiest day in American history.
- 1916 - World War I: Manfred von Richthofen ("The Red Baron"), a flying ace of the German Luftstreitkräfte, won his first aerial combat near Cambrai, France.
- 1928 - The Okeechobee Hurricane strikes southeastern Florida, killing upwards of 2,500 people. It is the third deadliest natural disaster in US history, behind the Galveston Hurricane of 1900 and the 1906 San Francisco earthquake.
- 1947 - James V. Forrestal was sworn in as the first Secretary of Defense of United States.
- 1948 - Lehi (also known as the Stern gang) assassinates Count Folke Bernadotte, who was appointed by the UN to mediate between the Arabs and Jews.
- 1978 - The Camp David Accords were signed by Israel and Egypt.
- 1980 - After weeks of strikes at the Lenin Shipyard in Gdańsk, Poland, the nationwide independent trade union Solidarity is established.
- 1991 - North Korea, South Korea, Estonia, Latvia, Lithuania, the Marshall Islands and Micronesia join the United Nations.