December 20 (December 20) is the 354th day of the year in the Gregorian calendar (355th in leap years). There are 11 days remaining until the end of the year.
69 - An army loyal to the Roman general Vespasian enters Rome and overthrows Emperor Vitellius.
1192 - Austrian Duke Leopold V captures King Richard the Lionheart of England on his return to England after making peace with Saladin.
1522 - During the siege of Rhodes, Suleiman the Magnificent accepts the surrender of the remaining Knights of Rhodes, whom he allows to be evacuated.
1582 - Gregorian calendar adopted in France.
1860 - South Carolina becomes the first federal state to secede from the United States.
1912 - A peace conference between Turkey and the Balkans begins in London, following the victory of the Balkan allies and the conquest of almost all Turkish possessions in Europe. The conference ended with the signing of the London Peace Treaty on May 30, 1913, by which Turkey renounced the European provinces to the Enos-Midi line, but the conflicts of the Balkan allies over the demarcation led to a new war.
1915 - The last Australian troops are evacuated from Gallipoli.
1917 - Cheka, the first Soviet secret police, is founded.
1924 - Adolf Hitler is released from Landsberg Prison.
1945 - Karl Renner is elected the first president of Austria's Second Republic.
1951 - The first experimental nuclear power plant in Idaho begins production.
1960 - The National Liberation Front of South Vietnam is founded, the communist political wing of the anti-American guerrilla forces Viet Viet.
1970 - Under pressure from workers 'unrest and strikes in Poland, the head of Poland's ruling United Workers' Party, Wladyslaw Gomulka, resigns. He was succeeded by Edward Gjerek.
1971 - Pakistani President Aga Mohammed Yaya Khan resigns following the defeat of Pakistani troops in the war with India in East Pakistan and hands over power to Zulfikar Ali Bhutto.
1986 - In the largest demonstrations since the beginning of the Cultural Revolution in China, more than 30,000 students protest in Shanghai demanding democratic freedoms.
1987 - A collision between the Philippine ferry Donja Paz and a tanker, the worst peacetime accident at sea, survives 24 of the 4,397 passengers and crew members of the ferry.
1989 - A 12,000-strong U.S. invasion of Panama begins