The United States and France signed the treaty creating their Revolutionary War alliance in 1778. The Treaty of Amity and Commerce and the Treaty of Alliance were signed in Paris on February 6, 1778.
France had supported the American cause secretly before the formal alliance, providing supplies, weapons, and money. The American victory at Saratoga in 1777 helped convince the French government that the rebellion had a realistic chance of defeating Britain. The treaty then brought French military and naval support into the open.
France’s alliance was crucial to the eventual American victory, especially during the Yorktown campaign. French forces fought alongside American forces on land, while the French navy helped prevent British relief. The alliance year is not the same as 1776, the year of the Declaration of Independence, or 1783, the year peace was concluded.