February 9 - By the terms of the Svalbard Treaty, international diplomacy recognizes Norwegian sovereignty over Arctic archipelago Svalbard, and designates it as demilitarized.
February 10 - Jozef Haller de Hallenburg performs symbolic wedding of Poland to the sea, celebrating restitution of Polish access to open sea.
February 13 - The Negro National League is formed.
February 14 - The League of Women Voters is founded in Chicago, Illinois.
March 13 - The Kapp Putsch briefly oust the Weimar Republic government from Berlin.
March 19 - The United States Senate rejects the Treaty of Versailles for the second time (first time was on November 19, 1919).
March 28 - Palm Sunday tornado outbreak of 1920 affects the Great Lakes region and Deep South states.
April 15 - Anarchists Sacco and Vanzetti allegedly murder two security guards while robbing a shoe store.
April 23 - The national council in Turkey denounces the government of Sultan Mehmed VI and announces a temporary constitution.
April 23 - The Grand National Assembly of Turkey is founded in Ankara.
April 28 - Azerbaijan is added to the Soviet Union.
April 30 - Peru becomes a signatory to the Buenos Aires copyright treaty.
May 2 - The first game of the Negro National League baseball is played in Indianapolis, Indiana.
May 5 - Nicola Sacco and Bartolomeo Vanzetti are arrested, accused of robbery and murder.
May 7 - Kiev Offensive (1920): Polish troops led by Józef Piłsudski and Edward Rydz-Śmigły and assisted by a symbolic Ukrainian force capture Kiev only to be driven out by the Red Army counter-offensive a month later.
May 7 - Treaty of Moscow (1920): Soviet Russia recognizes independence of the Democratic Republic of Georgia only to invade the country six months later.
May 9 - Polish-Soviet War: The Polish army under General Edward Rydz-Śmigły celebrates its capture of Kiev with a victory parade on Khreschatyk.
May 15 - Council of Lithuania adjourns as the newly elected Constituent Assembly of Lithuania meets for the first time in Kaunas.
May 16 - In Rome, Pope Benedict XV canonizes Joan of Arc as a saint.
May 20 - Montreal, Quebec radio station XWA broadcasts the first regularly scheduled radio programming in North America.
June 1 - Adolfo de la Huerta becomes president of Mexico.
June 4 - Hungary loses 71% of its territory and 63% of its population when the Treaty of Trianon is signed in Paris.
August 16 - Ray Chapman of the Cleveland Indians is hit in the head by a fastball thrown by Carl Mays of the New York Yankees, and dies early the next day. To date, Chapman is the second player to die from injuries sustained in a Major League Baseball game, the first being Doc Powers in 1909.
August 16 - The congress of the Communist Party of Bukhara opens. The congress would call for armed revolution.
August 18 - The Nineteenth Amendment to the United States Constitution is ratified, guaranteeing women's suffrage.
August 20 - The first commercial radio station, 8MK (WWJ), begins operations in Detroit, Michigan.
August 25 - Polish-Soviet War: Battle of Warsaw, which began on August 13, ends. The Red Army is defeated.
August 26 - The 19th amendment to United States Constitution takes effect, giving women the right to vote.
August 27 - Takes place the first radio broadcasting in Argentina.
August 31 - Polish-Bolshevik War: A decisive Polish victory in the Battle of Komarów.
August 31 - First radio news program broadcast by station 8MK in Detroit, Michigan.
September 16 - The Wall Street bombing: a bomb in a horse wagon explodes in front of the J.P.Morgan building in New York City
September 17 - The National Football League is organized in Canton, Ohio, United States.
October 1 - Sir Percy Cox landed in Basra to assume his responsibilities as high commissioner in Iraq.
October 10 - The Carinthian Plebiscite determines that the larger part of Carinthia should remain part of Austria.
October 14 - Part of Petsamo province is ceded by Soviet Union to Finland.
October 30 - The Communist Party of Australia is founded in Sydney.
November 1 - American Fishing Schooner Esperanto defeats the Canadian Fishing Schooner Delawana in the First International Fishing Schooner Championship Races in Halifax.
November 2 - In the United States, KDKA of Pittsburgh, Pennsylvania starts broadcasting as the first commercial radio station. The first broadcast was the results of the U.S. presidential election, 1920.
November 12 - Italy and the Kingdom of Serbs, Croats and Slovenes sign the Treaty of Rapallo.
November 15 - First assembly of the League of Nations is held in Geneva.
November 21 - Bloody Sunday during the Anglo-Irish War.
November 28 - Kilmichael Ambush, Battle of the Irish War of Independence.
December 2 - Following more than a month of Turkish-Armenian War, the Turkish dictated peace treaty is concluded -Treaty of Alexandropol
December 5 - Dimitrios Rallis forms a government in Greece.
December 16 - The Haiyuan earthquake, magnitude 8.5, rocks the Gansu province in China, killing an estimated 200,000.
December 22 - The GOELRO economic development plan is adopted by the 8th Congress of Soviets of the Russian SFSR.
