December 1st: In 1822, Dom Pedro is crowned as the first emperor of Brazil.

December 2nd: In 1804, Napoleon is crowned emperor of France.

December 3rd: In 1967, the first successful heart transplant took place in South Africa.

December 4th: In 1791, The Observer, the oldest Sunday Newspaper in the world is published.

December 5th: In 1492, Columbus discovers Haiti.

December 6th: In 1921, Ireland gained independence.

December 7th: In 1941, Japan attacked Pearl Harbour and brought the United States into World War 2.

December 8th: In 1980, music star John Lennon is assassinated.

December 9th: In 1608, British poet John Milton is born.

December 10th: In 1898, the Treaty of Paris is signed, ending the Spanish-American war with an American victory.

December 11th: In 1941, the Axis powers declare war on the US, and the US declares war on them in return.

December 12th: In 1901, the first transatlantic radio signal is sent.

December 13th: In 1642, New Zealand is discovered by Dutch navigators.

December 14th: In 1799, George Washington died at Mt. Vernon.

December 15th: In 1840, Napoleon is buried in Les Invalides in Paris.

December 16th: In 1773, the Boston Tea Party occured.

December 17th: In 1538, Pope Paul III excommunicated Henry VIII after he declared himself the head of the church of England. 

December 18th: In 1956, Japan joined the United Nations.

December 19th: In 1998, the House of Representatives impeached Bill Clinton.

December 20th: In 1860, South Carolina becomes the first state to declare secession from the United States of America.

December 21st: In 1992, the KGB is abolished.

December 22nd: In 1894, The United States Golf Association is founded.

December 23rd: In 1888, Vincent Van Gogh cut off his left ear.

December 24th: In 1990, On the bells of St. Basil’s Cathedral in Moscow rang for the first time since the death of Lenin.

December 25th: In 1066, William the Conqueror is crowned King of England.

December 26th: In 2004, an estimated 230,000 people were killed and 1.5 million left homeless when a magnitude 9.3 earthquake on the seafloor of the Indian Ocean set off a series of giant tsunami waves.

December 27th: In 1927, Leon Trotsky is expelled from the Communist Party.

December 28th: In 1856, Woodrow Wilson, 28th President of the United States is born.

December 29th: In 1916, Rasputin is assassinated.

December 30th: In 1862, during the American Civil War, the ironclad ship The Monitor sank.

December 31st: In 1879, Thomas Edison provided the first public demonstration of his electric incandescent lamp at his laboratory in Menlo Park, New Jersey.

Sources: 

https://www.historyplace.com/specials/calendar/december.htm