January 2 — The first Red Scare in the United States – 4025 suspected communists and anarchists are arrested and held without trial in several cities
January 7 – In the Russian Civil War, the forces of Russian White Admiral Alexander Kolchak surrender in Krasnoyarsk – the Great Siberian Ice March ensues
January 16 – Prohibition in the United States begins, with the Eighteenth Amendment to the Constitution coming into effect
February 2 – The Tartu Peace Treaty is signed, ending the Estonian War of Independence and recognizing the independence of both the Republic of Estonia and the Russian Socialist Federative Soviet Republic
February 7 — Admiral Kolchak and Viktor Pepelyayev are executed by firing squad near Irkutsk
February 17 — A woman named Anna Anderson tries to commit suicide in Berlin, and is taken to a mental hospital, where she claims she is Grand Duchess Anastasia of Russia
February 24 — Adolf Hitler presents his National Socialist Program in Munich to the German Workers’ Party (Deutsche Arbeiterpartei), which renames itself as the Nazi Party (Nationalsozialistische Deutsche Arbeiterpartei)
March 7 — The Syrian National Congress proclaims Syria independent, with Faisal I of Iraq as king
March 10 – The world’s first peaceful establishment of a social democratic government takes place in Sweden, as Hjalmar Branting takes over as Prime Minister
March 13—17 — Wolfgang Kapp and Walther von Lüttwitz’s Kapp Putsch (an attempted coup in Germany) briefly ousts the Weimar Republic government from Berlin, but fails due to public resistance and a general strike
March 15 — The Ruhr Red Army, a communist army 60,000 men strong, is formed in Germany
March 15—16 — Constantinople is occupied by British Empire forces, acting for the Allied Powers against the Turkish National Movement
March 19 — The United States Senate refuses to ratify the Treaty of Versailles
March 25 — British recruits to the Royal Irish Constabulary begin to arrive in Ireland. They become known from their improvised uniforms as the ‘Black and Tans’
April 4 — Violence erupts between Arab and Jewish residents in Jerusalem – 9 are killed, 216 injured
April 20 – The 1920 Summer Olympics open in Antwerp, Belgium. The Olympic symbols of five interlocking rings and the associated flag are first displayed at the games
April 23 — The Grand National Assembly of Turkey is founded by Mustafa Kemal Atatürk, in Ankara. It denounces the government of Sultan Mehmed VI, and announces a temporary constitution
May 2 — The first game of Negro National League baseball is played in Indianapolis
May 16 – Over 30,000 people attend the Canonization of Joan of Arc in Rome
May 20 — President Venustiano Carranza of Mexico arrives in San Antonio Tlaxcalantongo, where he is shot and killed by the troops of Rodolfo Herrero
June 4 — With the Treaty of Trianon, peace is restored between the Allied Powers and Hungary, which loses 72% of its territory
June 22 — In the Greek Summer Offensive, Greece attacks Turkish troops
July 19 — The Second Congress of the Communist International begins in Saint Petersburg and Moscow
July 24 — The French defeat the Syrian army at the Battle of Maysalun, occupy Damascus, and depose Faisal I of Syria as king
August 10 — Ottoman Sultan Mehmed VI’s representatives sign the Treaty of Sèvres with the Allied Powers, confirming arrangements for the partitioning of the Ottoman Empire
August 11 — Bolshevik Russia recognizes independent Latvia
August 19—25 — The Poles in Upper Silesia rise up against the Germans.
August 20 — The first commercial radio station in the United States, 8MK, begins operations in Detroit
August 26 — The Nineteenth Amendment to the United States Constitution is passed, guaranteeing women’s suffrage
September 16 — A bomb in a horse wagon explodes in front of the J. P. Morgan building in New York City, killing 38 and injuring 400
October 9 — In the Polish—Lithuanian War, Polish troops take Vilnius
November 2 – In the US presidential election, Republican Warren G. Harding defeats Democrat James M. Cox and Socialist Eugene V. Debs
November 13 — The White Army’s last units and civilian refugees are evacuated from the Crimea on board 126 ships
November 15 — In Geneva, the first assembly of the League of Nations is held
November 21 — The Irish Republican Army shoot dead 14 British undercover agents in Dublin. Later that day in retaliation, the Royal Irish Constabulary open fire on a crowd at a Gaelic Football match, killing 14
December 1 — The Mexican Revolution ends with a new regime coming to power, which couples with the end of the Old West
December 11 — British forces set fire to 5 acres of the centre of Cork, Ireland, including the City Hall, in reprisal attacks, after a British auxiliary is killed in a guerilla ambush
December 16 – An 8.6 Richter scale Haiyuan earthquake causes a landslide in Gansu Province, China, killing 180,000
December 22 — The 8th Congress of Soviets of the Russian SFSR adopts the GOELRO plan, the major plan of the economical development of the country