France became the United States’ formal ally through the 1778 Treaty of Alliance during the Revolutionary War.
The Treaty of Alliance was signed in Paris on February 6, 1778, alongside the Treaty of Amity and Commerce. France recognized the United States and agreed to cooperate militarily against Great Britain. The alliance followed the American victory at Saratoga in 1777.
French assistance included troops, weapons, money, naval forces, and military expertise. French naval participation was especially important during the Yorktown campaign, when the French fleet helped prevent British relief by sea.
France’s alliance should not be confused with earlier secret French aid or with Spain’s later entry into the war against Britain in 1779. French support was central to the American victory, although the United States remained responsible for its own army and political leadership.