September 20th

2011
The official US military policy of "don't ask, don't tell" ends. The policy was instituted by the administration of Bill Clinton in 1994. Under the policy, openly gay personnel were not allowed to serve in the United States military, but they could serve as long as they did not reveal their LGBT status.
Don't ask, don't tell
2001
American President, George W. Bush Declares War on Terror. The global military campaign against terrorism was first declared in the aftermath of the September 11 attacks in the United States. The phrase was used by President Bush in a speech given to the United States Congress.
War on Terror
2000
Independent Counsel Robert Ray announced the end of the Whitewater investigation, saying there was insufficient evidence to charge President Clinton and his wife, Hillary.
White House travel office controversy
1998
Baltimore Oriole shortstop Cal Ripken, Jr., sat out a game, ending his consecutive game playing streak. Ripken played 2,632 consecutive games over 16 seasons.
Cal Ripken Jr.
1990
Both East and West Germany ratify reunification.
German reunification
1984
The Cosby Show Airs for the First Time. The popular television sitcom followed the lives of a Brooklyn-based African-American family called the Huxtables. The show ran for 8 years on NBC and was largely based on the stand up comedy of Bill Cosby, who played the role of Heathcliff "Cliff" Huxtable, the father in the show.
The Cosby Show
1973
Billie Jean King Wins the Battle of the Sexes. The mixed gender tennis match between top tennis player Bobby Riggs and Billie Jean King was held in Houston, Texas after Riggs won another mixed gender match against Margaret Court earlier in the year. The matches were prompted by Riggs’ comments that even at an age of 55, he could beat any female tennis player. King beat Riggs and took home the $100,000 prize money. The match was and still is one of the most viewed tennis matches on television - it was watched by about 90 million people around the world.
Battle of the Sexes (tennis)
1904
Wilbur Wright Makes the First Circular Flight. Wright, who with his brother Orville, is credited for inventing the first airplane, made a complete circle in 1 minute and 16 seconds on the Wright Flyer II.
Wright Flyer II
1881
Chester A. Arthur was sworn in as the 21st president of the United States, succeeding James A. Garfield, who had been assassinated.
Chester A. Arthur
1870
Victor Emmanuel II, the first king of modern Italy, seized the Papal States from the French.
Papal States
1854
Battle of the Alma: first major battle of Crimean War. British and French alliance defeat the Russians.
Crimean War
1519
Spanish expedition led by Portuguese navigator Ferdinand Magellan sets off on the 1st successful circumnavigation of the globe (Magellan killed on route).
Ferdinand Magellan
622
Islamic Prophet Muhammed/Abu Bakr arrives in Jathrib (Medina).
Jewish tribes of Arabia
451
Roman General Flavius Aetius defeats Attila the Hun at The Battle of the Catalaunian Plainsat (Chalons-sur-Marne), halting Hun invasion of Roman Gaul.
Flavius Aetius