-The Washington Treaties are created in an attempt to halt the naval race by limiting the relative tonnage of rival battle fleets.

-The Red Scare errupts. U.S. Attorney-General A. Mitchell Palmer orders Justice Department raids on meeting halls and homes in 30 cities nationwide to round up all suspected communists. 2,700 people arrested without being charged with any explicit crime. In all, more than 6,000 are arrested. The raids end after a May 5 government ruling that mere membership in the party was not in itself a crime. Most arrested are released; few real anarchist criminals are found. Hysterical propaganda by Palmer and others set the tone for the rest of the twenties, spurring a spate of anti-immigration laws.

-On the heels of a decade of strikes, the twenties mark another period of constant, and often massive labor
disruptions. A huge garment workers strike begins in New York City. Before the decade ends, practically every trade, some more than once, would strike.

-The League of Nations first meets in Paris.

-Prohibition begins. The 18th Amendment to the U.S. Constitution goes into effect, prohibiting the making, selling, possession and consumption of alcoholic beverages. The most flouted law in history was repealed in 1933.

-Germany in chaos: An attempted overthrow of the unpopular Weimar Republic, the target of ongoing insurrections, general strikes and takeover attempts, occurs in Berlin. Known as the "Kapp Putsch," it forces the Berlin government into brief exile in Stuttgart for five days until the overthrow collapses.

-U.S. Senate refuses to join the League of Nations or ratify the Treaty of Versailles.

-The 'red scare' continues: Five legitimately elected members of the New York state legislature are expelled for being members of the Socialist Party.

-The Immigration Act is amended, allowing for deportation of anarchists and aliens advocating terrorism.

-Mohandas (later, Mahatma) Gandhi begins national campaign to rally the populace of India to use passive resistance and noncooperation against the occupying British colonialist government. The action is prompted by an earlier massacre of Indians and is also a protest against strict British laws clamping down on political activities.

-Womens' Suffrage victorious. The 19th Amendment to the U.S. Constitution adopted - allowing women the right to vote.

-Democratic leadership ends in U.S. with the election of Republicans Warren G. Harding and Calvin Coolidge to the presidency and vice presidency. A period of laissez-faire capitalism begins.

-Treaty of Sèvres dissolves Ottoman Empire.

-Palestine becomes a British mandate.

-Mexican president Venustiano Carranza is assassinated.

-Pan-African Congresses in Paris; anti-colonial unrest, African nationalism gains strength especially among black missionaries and Western-educated elites; unrest and strikes in Sierra Leone, the Gold Coast, and Nigeria of British West Africa.

-The Australia Country Party is formed.

-New Zealand joins the League of Nations.

-F. Scott Fitzgerald's This Side of Paradise, his first novel, is published.

-Main Street, Sinclair Lewis' critique of small-town America published; a key work in defining twenties attitudes that help usher in a slew of introspective, self-critical works about the American scene. It was the year's best seller.

-Soviet Russia issues Decree of Abortion; first nation to legalize the practice.

-Trojan condoms debut.

-Mystery writer Agatha Christie publishes her first novel, The Mysterious Affair at Styles.

-Edith Wharton's novel The Age of Innocence is published; would win the 1921 Pulitzer Prize.

-Rising popular interest in African-American literature sparks the beginning of the Harlem Renaissance.

-Speakeasies replace saloons as the center of social activity.

-Eugene O'Neill's Beyond the Horizon premieres
on Broadway; would later win the Pulitzer Prize for Drama.

-The pioneering German expressionist film Das Kabinett des Doktor Caligari (The Cabinet of Dr. Caligari) premieres.

-Premiere of D.W. Griffith's film melodrama Way Down East, starring Lillian Gish. It was one of the most profitable films of the twenties, earning 3.9 million dollars for United Artists.

-Composer Igor Stravinksy premieres his ballet 'Pulcinella' in France.

-Maurice Ravel composes 'La Valse'.

-Boston Red Sox star Babe Ruth sold to the New York Yankees for 125,000 dollars, the biggest trade deal in baseball up to that time.

-William T. "Big Bill" Tilden wins the first of his three Wimbledon titles, and dominates men's tennis for the rest of the decade, winning the U.S. Open seven times (1920-1925 and 1929).

-Water skiing invented at Lake Annecy in Haute Savoie, France.

-Finnish distance runner Paavo Nurmi wins the 10,000-meter run in record time at the 1920 Olympic Games at Antwerp. From 1920 to 1928, he netted six gold medals, among other track titles and records, and became the dominant runner of the decade.

-"Shoeless" Joe Jackson and 7 other members of the Chicago White Sox baseball team are accused of conspiring to lose the 1919 World Series as part of a deal with gamblers. On September 28, 1920, three players confessed and implicated the other five before a grand jury. On Nov. 12, 1920, Judge Kenesaw Mountain Landis is appointed baseball commissioner, and is granted dictatorial control to restore the game's reputation. On August 2, 1921, a Chicago jury acquits the players of wrongdoing, but commissioner Landis ignores the court and bans Jackson and other Chicago players from baseball forever.

-The 1920 Summer Olympics are held in Antwerp.

Physicist Albert Einstein arrives in New York to lecture at Columbia University on his theory of relativity.

-"The Tommy Gun," the Thompson portable submachine gun (invented by J.T. Thompson), is demonstrated at a national gun show in Ohio. Soon to become the weapon of choice for bootlegging gangsters.

-Nobel Prize for Chemistry won by Germany's Walther Nermst for his research on thermochemistry.

-U.S. scientist A.A. Michelson becomes first to measure the diameter of a distant star, Betelgeuse.