The American Revolutionary War began in April 1775 with fighting at Lexington and Concord, and the Continental Congress formally declared independence in July 1776. The war's early years were difficult for the American cause: George Washington's Continental Army suffered a serious defeat at the Battle of Long Island in August 1776, and was forced into a desperate retreat that, according to multiple documented accounts, was saved from complete disaster only by a fortunate, unusually heavy fog that concealed Washington's army as it evacuated across the East River to Manhattan, allowing it to escape a British force that could plausibly have captured or destroyed it entirely.
The war's turning point is generally identified as the October 1777 American victory at Saratoga, which convinced France — already providing covert support to the American cause — to enter the war openly as an American ally in 1778, bringing crucial military, naval, and financial support that proved decisive to the war's eventual outcome. The war's final major engagement, the Siege of Yorktown in 1781, saw combined American and French forces trap and force the surrender of a major British army under Lord Cornwallis, a defeat that led directly to British peace negotiations and the 1783 Treaty of Paris formally recognizing American independence.