| 137821 | December 6 | Event | 1916 – World War I: The Central Powers capture Bucharest. |
| 137822 | December 6 | Event | 1917 – Finland declares independence from Russia. |
| 137823 | December 6 | Event | 1917 – Halifax Explosion: A munitions explosion near Halifax, Nova Scotia kills more than 1,900 people in the largest artificial explosion up to that time. |
| 137824 | December 6 | Event | 1917 – World War I: USS Jacob Jones is the first American destroyer to be sunk by enemy action when it is torpedoed by German submarine SM U-53. |
| 137825 | December 6 | Event | 1921 – The Anglo-Irish Treaty is signed in London by British and Irish representatives. |
| 137826 | December 6 | Event | 1922 – One year to the day after the signing of the Anglo-Irish Treaty, the Irish Free State comes into existence. |
| 137827 | December 6 | Event | 1928 – The government of Colombia sends military forces to suppress a month-long strike by United Fruit Company workers, resulting in an unknown number of deaths. |
| 137828 | December 6 | Event | 1933 – U.S. federal judge John M. Woolsey rules that James Joyce's novel Ulysses is not obscene. |
| 137829 | December 6 | Event | 1941 – World War II: The United Kingdom and Canada declare war on Finland in support of the Soviet Union during the Continuation War. |
| 137830 | December 6 | Event | 1947 – The Everglades National Park in Florida is dedicated. |
| 137831 | December 6 | Event | 1953 – Vladimir Nabokov completes his controversial novel Lolita. |
| 137832 | December 6 | Event | 1956 – A violent water polo match between Hungary and the USSR takes place during the 1956 Summer Olympics in Melbourne, against the backdrop of the 1956 Hungarian Revolution. |
| 137833 | December 6 | Event | 1957 – Project Vanguard: A launchpad explosion of Vanguard TV3 thwarts the first United States attempt to launch a satellite into Earth orbit. |
| 137834 | December 6 | Event | 1967 – Adrian Kantrowitz performs the first human heart transplant in the United States. |
| 137835 | December 6 | Event | 1969 – Meredith Hunter is killed by Hells Angels during a Rolling Stones concert at the Altamont Speedway in California. |
| 137836 | December 6 | Event | 1971 – Pakistan severs diplomatic relations with India following New Delhi's recognition of Bangladesh. |
| 137837 | December 6 | Event | 1973 – The Twenty-fifth Amendment: The United States House of Representatives votes 387 to 35 to confirm Gerald Ford as Vice President of the United States. (On November 27, the Senate confirmed him 92 to 3.) |
| 137838 | December 6 | Event | 1975 – The Troubles: Fleeing from the police, a Provisional IRA unit takes a couple hostage in Balcombe Street, London, beginning a six-day siege. |
| 137839 | December 6 | Event | 1977 – South Africa grants independence to Bophuthatswana, although it is not recognized by any other country. |
| 137840 | December 6 | Event | 1978 – Spain approves its latest constitution in a referendum. |
| 137841 | December 6 | Event | 1982 – The Troubles: The Irish National Liberation Army bombed a pub frequented by British soldiers in Ballykelly, Northern Ireland. It killed eleven soldiers and six civilians. |
| 137842 | December 6 | Event | 1988 – The Australian Capital Territory is granted self-government. |
| 137843 | December 6 | Event | 1989 – The École Polytechnique massacre (or Montreal Massacre): Marc Lépine, an anti-feminist gunman, murders 14 young women at the École Polytechnique in Montreal. |
| 137844 | December 6 | Event | 1991 – In Croatia, forces of the Yugoslav People's Army bombard Dubrovnik after laying siege to the city since May. |
| 137845 | December 6 | Event | 1992 – The Babri Masjid in Ayodhya, India, is demolished, leading to widespread riots causing the death of over 1,500 people. |
| 137846 | December 6 | Event | 1997 – A Russian Antonov An-124 cargo plane crashes into an apartment complex near Irkutsk, Siberia, killing 67. |
| 137847 | December 6 | Event | 2005 – Several villagers are shot dead during protests in Dongzhou, China. |
| 137848 | December 6 | Event | 2005 – An Iranian Air Force C-130 military transport aircraft crashes into a ten-floor apartment building in a residential area of Tehran, killing all 84 on board and 44 more on the ground. |
| 137849 | December 6 | Event | 2006 – NASA reveals photographs taken by Mars Global Surveyor suggesting the presence of liquid water on Mars. |
| 137850 | December 6 | Event | 2008 – The 2008 Greek riots break out upon the killing of a 15-year-old boy, Alexandros Grigoropoulos, by a police officer. |