Following the American Revolution, Evacuation Day on November 25 marks the day in 1783 when the last vestige of British authority in the United States — its troops in New York — departed from Manhattan. The last shot of the American Revolutionary War was reported to be fired on this day, as a British gunner on one of the departing ships fired a cannon at jeering crowds gathered on the shore of Staten Island, at the mouth of New York Harbor (the shot fell well short of the shore).
Carleton gave a final evacuation date of noon on November 25. Entry into the city by George Washington was delayed until after a British flag had been removed. A Union Flag was nailed on a flagpole in the Battery Park at the southern tip of Manhattan. The pole was allegedly greased. After a number of men attempted to tear down the British color - a symbol of tyranny for contemporary American Patriots - wooden cleats were cut and nailed to the pole and with the help of a ladder, a veteran, John Van Arsdale, was able to ascend the pole, remove the flag, and replace it with the Stars and Stripes before the British fleet had sailed out of sight. General George Washington led the Continental Army in a triumphal march down Broadway to the Battery immediately afterward.
For over a century this event was commemorated annually with boys competing to tear down a Union Flag from a greased pole in Battery Park, as well as the anniversary in general being celebrated with much adult revelry and corresponding beverages. But the wider national observance of the date began to wane after Abraham Lincoln, in his October 3, 1863, Thanksgiving Day Proclamation, called on Americans "in every part of the United States, and also those who are at sea and those who are sojourning in foreign lands, to set apart and observe the last Thursday of November next as a day of thanksgiving."
Wikipedia - http://en.wikipedia.org/wiki/Evacuation_Day_%28New_York%29