1.1777: The Battle of White Marsh, a Revolutionary War battle fought near Philadelphia, PA, ended on December 21, 1777. It was a victory for the Continental Army, who successfully repelled a British attack.

2.1837: On December 21, 1837, John Greenleaf Whittier's anti-slavery poem "The Pennsylvania Pilgrim" was first published in the Pennsylvania Freeman newspaper. The poem was later included in Whittier's collection "Voices of Freedom" and became a popular abolitionist text.

3.1896: The first meeting of the Pennsylvania State Dental Society was held on December 21, 1896 in Harrisburg, PA. The organization was founded to promote the dental profession and improve oral health in the state.

4.1937: On December 21, 1937, the film "Snow White and the Seven Dwarfs" premiered at the Radio City Music Hall in New York City. The animated film, produced by Walt Disney Productions, was based on the popular fairy tale and became a classic in American cinema.

5.1971: The Philadelphia Flyers played their first game at the newly-opened Spectrum arena on December 21, 1971. The Flyers defeated the Pittsburgh Penguins 1-0 in front of a sold-out crowd of over 17,000 fans. The Spectrum was home to the Flyers for over 30 years before its demolition in 2011.