9th January » Greco-Turkish War (1919–1922) known as Greco-Turkish War: The First Battle of İnönü, the first battle of the war, begins near Eskişehir in Anatolia.
20th January » Turkish Constitution of 1921 called The first Constitution of Turkey is adopted, making fundamental changes in the source and exercise of sovereignty by consecrating the principle of national sovereignty.
15th February » Kingdom of Romania establishes its legation in Helsinki.
20th February » The Young Communist League of Czechoslovakia is founded.
21st February » Rezā Shāh takes control of Tehran during a Iranian events of 1921 named successful coup
22nd February » After Russian forces under Baron Roman von Ungern-Sternberg drive the Chinese out, the Bogd Khan is reinstalled as the khan (title) called emperor of Mongolia.
25th February » Tbilisi, capital of the Democratic Republic of Georgia, is Soviet invasion of Georgia called occupied by Russian Soviet Federative Socialist Republic called Bolshevist Russia.
27th February » The International Working Union of Socialist Parties is founded in Vienna.
1st March » The Australia national cricket team called Australian cricket team captained by Warwick Armstrong becomes the first team to complete a whitewash (sport) called whitewash of The Ashes, something that would not be repeated for 86 years.
6th March » Portuguese Communist Party is founded as the Portuguese Section of the Comintern e.g Communist International.
8th March » Spain Spanish Prime Minister of Spain Premier Eduardo Dato Iradier is assassinated while exiting the Cortes Generales parliament building in Madrid.
12th March » İstiklal Marşı was adopted in TBMM(Turkish grand national assembly).
13th March » Mongolia is proclaimed an independent monarchy, ruled by Russian military officer Roman von Ungern-Sternberg as a dictator.
17th March » The Second Republic of Poland adopts the March Constitution.
18th March » The second Peace of Riga is signed between Poland and the Soviet Union.
19th March » Irish War of Independence: One of Crossbarry Ambush known as the biggest engagements of the war takes place at Crossbarry, County Cork. About 100 Irish Republican Army (IRA) volunteers escape an attempt by over 1,300 British forces to encircle them.
21st March » The New Economic Policy is implemented by the Bolshevik Party in response to the economic failure as a result of War Communism.
31st March » The Royal Australian Air Force is formed.
2nd April » The Autonomous Government of Khorasan, a military government encompassing the modern state of Iran, is established.
11th April » Emir Abdullah I of Jordan named Abdullah establishes the first centralised government in the newly created British protectorate of Emirate of Transjordan known as Transjordan.
15th April » Black Friday (1921) named Black Friday: mine owners announce more wage and price cuts, leading to the threat of a strike all across England.
3rd May » West Virginia becomes the first state to legislate a broad sales tax, but does not implement it until a number of years later due to enforcement issues.
19th May » The United States Congress passes the Emergency Quota Act establishing national quotas on immigration.
31st May » Tulsa race riot: Civil disorder named civil unrest in Tulsa, Oklahoma. The official death toll is 39, but recent investigations suggest the actual toll may be much higher.
1st June » Tulsa Race Riot: civil unrest in Tulsa, Oklahoma.
6th June » Southwark Bridge in London is opened to traffic by King George V and Mary of Teck known as Queen Mary.
20th June » Workers of Buckingham and Carnatic Mills in the city of Chennai, India, begin a 1921 Buckingham and Carnatic Mills Strike or four-month strike.
28th June » Serbian King Alexander I of Serbia known as Alexander I proclaimed the new constitution of the Kingdom of Serbs, Croats and Slovenes, known thereafter as the Vidovdan Constitution.
30th June » U.S. President Warren G. Harding appoints former President William Howard Taft Chief Justice of the United States.
1st July » The Communist Party of China is founded.
2nd July » World War I: President of the United States called U.S. President Warren G. Harding signs the Knox–Porter Resolution formally ending the war between the United States and Imperial Germany.
11th July » A truce in the Irish War of Independence comes into effect.
11th July » Former President of the United States William Howard Taft is sworn in as 10th Chief Justice of the United States or Chief Justice of the Supreme Court of the United States known as U.S. Supreme Court, becoming the only person ever to hold both offices.
27th July » Researchers at the University of Toronto led by biochemist Frederick Banting prove that the hormone insulin regulates blood sugar.
29th July » Adolf Hitler becomes leader of the Nazi Party or National Socialist German Workers Party.
3rd August » Commissioner of Baseball named Major League Baseball Commissioner Kenesaw Mountain Landis confirms the ban of the eight Black Sox Scandal called Chicago Black Sox, the day after they were acquitted by a Chicago court.
23rd August » British R38 class airship e.g airship R-38 experiences structural failure over Kingston upon Hull or Hull in England and crashes in the Humber estuary. Of her 49 British and American training crew, only four survive.
25th August » The first skirmishes of the Battle of Blair Mountain occur.
27th August » The British install the son of Hussein bin Ali, Sharif of Mecca Sharif Hussein bin Ali (leader of the Arab Revolt of 1916 against the Ottoman Empire) as Faisal I of Iraq King Faisal I of Kingdom of Iraq Iraq.
5th September » Roscoe "Fatty" Arbuckle party in San Francisco ends with the death of the young actress Virginia Rappe: One of the first scandals of the Hollywood community.
7th September » In Atlantic City, New Jersey, the first Miss America Pageant, a two-day event, is held.
7th September » The Legion of Mary, the largest Consecrated life Apostolic congregations named apostolic organization of lay people in the Catholic Church, is founded in Dublin, Ireland.
11th September » Nahalal, the first moshav in Palestine, is settled as part of a Zionist plan to colonize Palestine and creating a Jewish state, later to be Israel.
21st September » A storage silo in Ludwigshafen or Oppau, Germany, Oppau explosion known as explodes, killing 500-600 people.
5th October » Baseball: The World Series is broadcast on the radio for the first time.
13th October » The Soviet republics of Russian Soviet Federative Socialist Republic Russia, Armenian Soviet Socialist Republic Armenia, Azerbaijan Soviet Socialist Republic Azerbaijan, and Georgian Soviet Socialist Republic Georgia sign the Treaty of Kars with the Grand
18th October » The Crimean Autonomous Soviet Socialist Republic is formed as part of the Russian Soviet Federative Socialist Republic.
19th October » Portuguese Prime Minister António Granjo and other politicians are murdered in a Lisbon Bloody Night called coup.
21st October » President Warren G. Harding delivers the first speech by a sitting U.S. President against lynching in the deep South.
29th October » The Link River Dam, a part of the Klamath Reclamation Project, is completed.
29th October » Second trial of Sacco and Vanzetti in the United States of America.
29th October » The Harvard University football team loses to Centre College, ending a 25 game winning streak. This is considered one of the biggest upsets in college football.
4th November » Prime Minister of Japan e.g Japanese Prime Minister Hara Takashi is assassinated in Tokyo.
4th November » The Milite Ignoto e.g Italian unknown soldier is buried in the Altare della Patria (Fatherland Altar) in Rome.
9th November » The Partito Nazionale Fascista (PNF), National Fascist Party, comes into existence.
11th November » The Tomb of the Unknowns is dedicated by President of the United States known as US President Warren G. Harding at Arlington National Cemetery.
14th November » Foundation of the Communist Party of Spain.
4th December » The first Virginia Rappe manslaughter trial against Roscoe Arbuckle known as Roscoe "Fatty" Arbuckle ends in a hung jury.
6th December » The Anglo-Irish Treaty is signed in London by British and Irish representatives.
23rd December » Visva-Bharati University is inaugurated.