December 20th

Queen Elizabeth becomes the longest-living British monarch. The previous longest living monarch - Queen Victoria - died on Jan 22, 1901, when she was 81 years, 7 months, and 29 days old. Queen Elizabeth, who was born on 21 April 1926, turned 81 years, 7 months and 30 days on this day.
Elizabeth II
Portuguese transfer sovereignty of Macau to China. Portugal ruled over the special administrative region of China from the mid-16th century to 1999. Macau has a high degree of independence from China, and has control over its legal system, monetary system, and immigration policy.
Transfer of sovereignty over Macau
Astronomer Carl Sagan died at age 62.
Carl Sagan
United States' invasion of Panama begins. Also known as Operation Just Cause, the invasion took place under the leadership of President George H. W. Bush and led to the deposing of the dictator, Manuel Noriega. The invasion ended on January 31, 1990.
United States invasion of Panama
Spanish Prime Minister Carrero Blanco assassinated. A confidant of dictator Francisco Franco, Blanco was assassinated by the Basque nationalist and separatist group Euskadi Ta Askatasuna or ETA.
Luis Carrero Blanco
Author John Steinbeck died at age 66.
John Steinbeck
Cheka formed - Soviet state security force and forerunner to the KGB, under Felix Dzerzhinsky after decree by Lenin.
South Carolina became the first state to secede from the Union.
South Carolina in the American Civil War
'Grimm's Fairy Tales' by Jacob and Wilhelm Grimm is published.
Grimm's Fairy Tales
Louisiana Purchase completed. The United States was officially handed over the territory of Louisiana by the French. The French had regained control of the territory that spans over 15 present-day states and 2 Canadian territories in 1800. In 1762, Spain had taken over the territory.
Louisiana Purchase
Samuel Slater built the nation's first cotton mill in Pawtucket, R.I.
Samuel Slater
Virginia Company settlers leave London to establish Jamestown, Virginia.
Virginia Company
Suleiman the Magnificent accepts surrender of the surviving Knights of Rhodes, who are allowed to evacuate. Eventually settle in Malta, become known as the Knights of Malta.