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June 28, 1919 - The Treaty of Versailles is signed, ending World War I.
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January 10, 1920 - The League of Nations is established with the ratification of the Treaty of Versailles, ending the hostilities of the first World War. Nine days later the United States Senate votes against joining the League.
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May 19, 1921 - A national quota system on the amount of incoming immigrants is established by the United States Congress in the Emergency Quota Act, curbing legal immigration.
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February 6, 1922 - The Armaments Congress ends. It would lead to an agreement, the Five Power Disarmament Treaty, between the major world powers of the United Kingdom, France, Italy, Japan, and the United States, to limit naval construction, outlaw poison gas, restrict submarine attacks on merchant fleets and respect China's sovereignty.
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August 2, 1923 - President Warren G. Harding dies in office after becoming ill following a trip to Alaska, and is succeeded by his Vice President, Calvin Coolidge. Coolidge would oppose the League of Nations, but approved of the World Court.
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May 10, 1924 - J. Edgar Hoover is appointed to lead the Federal Bureau of Investigation.
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January 5, 1925 - Nellie Tayloe Ross is inaugurated as the first woman governor of the United States in Wyoming. Miriam Ferguson is installed two weeks later as the second during a ceremony in Texas.
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May 20, 1926 - Air Commerce Act is passed, providing aid and assistance to the airline industry, plus federal oversight under the Department of Commerce for civil air safety.
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March 5, 1927 - The civil war in China prompts one thousand United States marines to land in order to protect property of United States interests.
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November 6, 1928 - Herbert Hoover wins election as President of the United States with an Electoral College victory, 444 to 87 over Democratic candidate Alfred E. Smith, the Catholic governor of New York.