September 1 ( ):
- 1859 – British astronomers observed a major solar flare, which set off a geomagnetic storm that caused telegraph system failure throughout Europe and North America.
- 1939 – Germany and Slovakia invaded Poland, setting off World War II.
September 2 ():
September 3 ():
- 1783 – The Treaty of Paris was signed, which upon final approval by the Congress of the Confederation and the King of Great Britain, ended the American Revolutionary War.
September 4 ():
- 1781 – Los Angeles, California, is founded as El Pueblo de Nuestra Señora La Reina de los Ángeles de Porciúncula (The Village of Our Lady, the Queen of the Angels of Porziuncola) by 44 Spanish settlers.
- 1812 – War of 1812: The Siege of Fort Harrison begins when the fort is set on fire.
- 1862 – Civil War Maryland Campaign: General Robert E. Lee takes the Army of Northern Virginia, and the war, into the North.
- 1870 – Emperor Napoleon III of France is deposed and the Third Republic is declared.
- 1884 – The United Kingdom ends its policy of penal transportation to New South Wales in Australia.
- 1886 – Indian Wars: after almost 30 years of fighting, Apache leader Geronimo, with his remaining warriors, surrenders to General Nelson Miles in Arizona.
- 1888 – George Eastman registers the trademark Kodak and receives a patent for his camera that uses roll film.
- 1939 – World War II: a Bristol Blenheim is the first British aircraft to cross the German coast following the declaration of war and German ships are bombed.
- 1998 – Google is founded by Larry Page and Sergey Brin, two students at Stanford University.
September 5 ():
- 1798 – Conscription is made mandatory in France by the Jourdan law.
- 1836 – Sam Houston is elected as the first president of the Republic of Texas.
- 1877 – Indian Wars: Oglala Sioux chief Crazy Horse is bayoneted by a United States soldier after resisting confinement in a guardhouse at Fort Robinson in Nebraska.
- 1882 – Labor Day is observed for the first time in the United States by the Central Labor Union of New York.
- 1942 – World War II: Japanese high command orders withdrawal at Milne Bay, first Japanese defeat in the Pacific War.
- 1945 – Cold War: Igor Gouzenko, a Soviet Union embassy clerk, defects to Canada, exposing Soviet espionage in North America, signalling the beginning of the Cold War.
- 1978 – Camp David Accords: Menachem Begin and Anwar Sadat begin peace process at Camp David, Maryland.
September 6 ():
September 7 ():
- 1776 – World's first submarine attack: the American submersible craft Turtle attempts to attach a time bomb to the hull of British Admiral Richard Howe's flagship HMS Eagle in New York Harbor.
- 1864 – American Civil War: Atlanta, Georgia, is evacuated on orders of Union General William Tecumseh Sherman.
- 1876 – In Northfield, Minnesota, Jesse James and the James-Younger Gang attempt to rob the town's bank but are driven off by armed citizens.
- 1916 – Federal employees win the right to Workers' compensation by Federal Employers Liability Act (39 Stat. 742; 5 U.S.C. 751)
- 1927 – The first fully electronic television system is achieved by Philo Taylor Farnsworth.
- 1940 – World War II: The Blitz – Nazi Germany begins to rain bombs on London. This will be the first of 57 consecutive nights of bombing.
- 1945 – World War II: Japanese forces on Wake Island, which they had held since December of 1941, surrender to U.S. Marines.
- 1979 – The Entertainment and Sports Programming Network, better known as ESPN, makes its debut.
- 1979 – The Chrysler Corporation asks the United States government for USD $1.5 billion to avoid bankruptcy.
- 2005 – First presidential election is held in Egypt.
- 2008 – The US Government takes control of the two largest mortgage financing companies in the US, Fannie Mae and Freddie Mac.
September 9 ():
September 11 ():
- 1791 – Pennsylvanians defied the whiskey tax, tarring and feathering a tax collector.
- 1973 – With the backing of the US, Augusto Pinochet overthrew Salvador Allende's democratic government of Chile and established a military junta.
September 12 ():
September 13 ():
- 1994 – The Federal Assault Weapons Ban was enacted, banning the sale of a variety of semi-automatic firearms and "high-capacity" magazines.
September 14 ():
- 1940 – The US Congress passed the Selective Training and Service Act, which established the first peacetime conscription in US history.
September 16 ():
- 1838 – James J. Hill, the railroad executive behind the Great Northern Railway (the only privately funded railway in the United States), was born.
September 17 ():
September 19 ():
- 1796 – George Washington's Farewell Address was published, in which he argues for non-interventionism in foreign affairs.
September 20 ():
September 22 ():
- 1776 – Nathan Hale was hanged for espionage during the American Revolutionary War.
- 1862 – President Abraham Lincoln made a formal announcement of the Emancipation Proclamation, promising to free slaves in rebelling states.
September 24 ():
- 1917 – The Second Liberty Bond Act of 1917 was enacted, establishing the US debt limit in order to finance entry into World War I.
September 26 ():
- 1914 – The Federal Trade Commission was created with the power to stop what it deems unfair trade practices.
September 29 ():
September 30 ():