December 20 is the 354th day of the year in the Gregorian calendar. There are 11 days remaining until the end of the year.
AD 69 – Vespasian, formerly a general under Nero, enters Rome to claim the title of Emperor.
1192 – Richard I of England is captured and imprisoned by Leopold V of Austria on his way home to England after the Third Crusade.
1334 – Pope Benedict XII is elected.
1606 – The Virginia Company loads three ships with settlers and sets sail to establish Jamestown, Virginia, the first permanent English settlement in the Americas.
1803 – The Louisiana Purchase is completed at a ceremony in New Orleans.
1808 – Peninsular War: The Siege of Zaragoza begins.
1808 – The original Covent Garden Theatre in London is destroyed by a fire, along with most of the scenery, costumes and scripts.
1832 – HMS Clio under the command of Captain Onslow arrives at Port Egmont under orders to take possession of the Falkland Islands
1860 – South Carolina becomes the first state to attempt to secede from the United States.
1915 – World War I: The last Australian troops are evacuated from Gallipoli.
1917 – Cheka, the first Soviet secret police force, is founded.
1924 – Adolf Hitler is released from Landsberg Prison.
1941 – World War II: First battle of the American Volunteer Group, better known as the "Flying Tigers" in Kunming, China.
1942 – World War II: Japanese air forces bomb Calcutta, India.
1946 – The popular Christmas film It's a Wonderful Life is first released in New York City.
1948 – Indonesian National Revolution: The Dutch military captures Yogyakarta, the temporary capital of the newly-formed Republic of Indonesia.
1951 – The EBR-1 in Arco, Idaho becomes the first nuclear power plant to generate electricity. The electricity powered four light bulbs.
1952 – A United States Air Force C-124 crashes and burns in Moses Lake, Washington killing 87.
1955 – Cardiff is proclaimed the capital city of Wales, United Kingdom.
1957 – The initial production version of the Boeing 707 makes its first flight.
1967 – A Pennsylvania Railroad Budd Metroliner exceeds 155 mph on their New York Division, also present day Amtrak's Northeast Corridor.
1968 – The Zodiac Killer kills Betty Lou Jenson and David Faraday in Vallejo, California.
1971 – The international aid organization Doctors Without Borders is founded by Bernard Kouchner and a group of journalists in Paris, France.
1973 – The Prime Minister of Spain, Admiral Luis Carrero Blanco, is assassinated by a car bomb attack in Madrid.
1984 – The Summit Tunnel fire, one of the largest transportation tunnel fires in history, burns after a freight train carrying over one million liters of gasoline derails near the town of Todmorden, England, in the Pennines.
1985 – Pope John Paul II announces the institution of World Youth Day.
1987 – In the worst peacetime sea disaster, the passenger ferry Doña Paz sinks after colliding with the oil tanker Vector in the Tablas Strait in the Philippines, killing an estimated 4,000 people (1,749 official).
1989 – The United States invasion of Panama deposes Manuel Noriega.
1991 – A Missouri court sentences the Palestinian militant Zein Isa and his wife Maria to death for the honor killing of their daughter Palestina.
1995 – NATO begins peacekeeping in Bosnia.
1995 – American Airlines Flight 965, a Boeing 757, crashes into a mountain 50 km north of Cali, Colombia killing 159.
1999 – Macau is handed over to China by Portugal.
2004 – A gang of thieves steal £26.5 million worth of currency from the Donegall Square West headquarters of Northern Bank in Belfast, Northern Ireland, United Kingdom, one of the largest bank robberies in British history.
2007 – Elizabeth II becomes the oldest monarch of the United Kingdom, surpassing Queen Victoria, who lived for 81 years, seven months and 29 days.
2007 – The Portrait of Suzanne Bloch (1904), by the Spanish artist Pablo Picasso, and O Lavrador de Café by Brazilian modernist painter Cândido Portinari, are stolen from the São Paulo Museum of Art.