- Sep 1 Annie Besant founds the India Home Rule League
- Sep 1 Bulgaria declares war on Romania
- Sep 1 US Keating-Owen Act bans child labor banned from interstate commerce
- Sep 3 Battle of Verdun: French counterattacks on German flanks push their frontline further from the town
Adamson Act
Sep 3 US President Woodrow Wilson signs Adamson Act, providing an 8-hour day on interstate railroads, preventing a national railroad strike
- Sep 4 Future Baseball Hall of Fame pitchers Christy Mathewson & Mordecai Brown face each other for a final time; after 25 contests Mathewson takes a 13-12 advantage with Reds 10-8 winners over Cubs
Intolerance
Sep 5 "Intolerance", silent film directed by D. W. Griffith, starring Vera Lewis and Ralph Lewis, is released
US Men's Tennis Open
Sep 5 US National Championship Men's Tennis: R. Norris Williams beats Bill Johnston 4-6, 6-4, 0-6, 6-2, 6-4 for his 2nd and final US singles crown
First Supermarket
Sep 6 1st true supermarket, the "Piggly Wiggly" is established by Clarence Saunders in Memphis, Tennessee, grand opening delayed by construction until the 11th
- Sep 7 Giants beat Brooklyn 4-1, to launch NY's record 26-game winning streak
- Sep 7 Workmen's Compensation Act passed by US Congress
- Sep 8 US President Woodrow Wilson signs the Emergency Revenue Act, doubling the rate of income tax and adding inheritance and munitions profits tax
- Sep 11 Clarence Saunders opens "Piggly Wiggly" - the 1st self-service supermarket, in Memphis, Tennessee
- Sep 11 German troops conquer Kavalla, Greece
- Sep 11 The Quebec Bridge's central span collapses during reconstruction, killing 11 men
- Sep 14 Christy Mathewson pitches & wins his final game
1st Use of Tanks in War
Sep 15 First use of tanks in warfare, "Little Willies" at Battle of Flers-Courcelette, part of the Battle of the Somme
- Sep 17 40,000 Amsterdam demonstrators demand general voting right
The Red Baron
Sep 17 WWI flying ace The Red Baron of the German Luftstreitkräfte, wins his first aerial combat near Cambrai, France
- Sep 19 Belgian troops conquer Tabora, German East Africa
- Sep 19 First landing at Schiphol Airport, Netherlands (Farman F-22 of Soesterberg)
- Sep 24 Indians' Marty Kavanaugh, hits AL's 1st pinch-hit grand slam
- Sep 26 Bishop speak against Catholics in trade unions
- Sep 27 1st Native American Day celebrated, honoring American Indians
- Sep 27 Emperor Lidj Jasu of Ethiopia flees a palace coup led by his aunt Zauditu
World's 1st Billionaire
Sep 29 American oil tycoon John D. Rockefeller becomes the world's first billionaire
Provisional Government of National Defence
Sep 30 Eleftherios Venizelos announces he is forming a Provisional Government in Crete as an alternative to the one in Athens; he is determined to bring Greece into the war on the side of the Allies
- Sep 30 Giants lose to Braves 8-3, ends 26 consecutive win streak
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