1920 16 January. The 18th Amendment (Prohibition Amendment) goes into effect at midnight. Although the law is challenged in some states (New Jersey), the Supreme Court later declares the law valid.
The 19th Amendment (voting rights for women) goes into effect.
2 November. Station KDKA in Pittsburgh, Pennsylvania, initiates regular radio broadcasts, the first station to do so.
1921 The Emergency Quota Act restricts immigration by setting limits based on the number of foreign-born people already in the country in 1910. Immigration must not exceed three percent of each nationality already in the United States in that year.
Former president William Howard Taft is appointed to the Supreme Court.
July-September. Wage cuts and massive unemployment cause unrest and an increase in violence. The newly formed Hoover Commission suggests price cuts and shorter hours rather than an increase in wages; the average working day is 12-14 hours.
1922 The Supreme Court declares the 19th Amendment (votes for women) to be constitutional.
1923 2 August. President Harding dies of an embolism after suffering ptomaine poisoning followed by pneumonia. Coolidge is sworn in on 3 August.
1924 Congress passes a new and more restrictive immigration law; quotas are now set at only 2 percent of existing nationalities in the U.S. in 1920, and Japanese immigration is suspended.
Calvin Coolidge is elected by a large margin over the Democratic candidate, John W. Davis, and the Progressive candidate, Robert La Follette.
1925 February. A diphtheria epidemic in Alaska captures the country's attention as dog teams drive through the winter weather to deliver antidiphtheria serum to Nome.
July. The Scopes trial begins as John T. Scopes of Tennessee is arrested for teaching Darwin's theory of evolution. Clarence Darrow defends Scopes as William Jennings Bryan heads the prosecution. In an unusual move, Bryan takes the witness stand to defend his strict interpretation of the Bible. Scopes loses the trial and is fined $100, but the trial publicity has given the debate over evolution national attention
1926 Richard Byrd makes the first flight over the North Pole.
Gertrude Ederle, daughter of a New York delicatessen owner, is the first to swim the treacherous twenty-two-mile English Channel in fourteen hours and thirty-one minutes. A feat that earned her a New York City ticker tape parade.
1927
20-21 May. Charles Lindbergh flies The Spirit of St. Louis from New York to Paris, traveling 3600 miles in 33 and a half hours.
Refusing a nomination for reelection in what will become a famous statement, Calvin Coolidge says, "I do not choose to run."
October. The Jazz Singer, starring Broadway star Al Jolson, debuts as the "first" talking picture, and its success spells the beginning of the end for silent movies.
1928 Elections: In the presidential election, Republican Herbert Hoover, whose party's slogan is "A chicken in every pot, a car in every garage," beats Democratic candidate Al Smith. Democrat Franklin D. Roosevelt is elected governor of New York.
1929 14 February. In the "St. Valentine's Day Massacre," six gangsters from the "Bugs" Moran mob and another man are gunned down in a Chicago garage.
24-29 October. On "Black Thursday," 24 October, 13 million shares are sold on the New York Stock Exchange; despite efforts to shore up prices by J. P. Morgan and John D. Rockefeller, prices fall again on 29 October, "Black Tuesday," as 16 million shares are sold. By 13 November, $30 billion has been lost in devalued stocks. Although all of the effects are not felt immediately, the stock market crash marks the beginning of the Great Depression.