France became the United States’ formal military ally in 1778 during the Revolutionary War.
The Franco-American Alliance was established by the Treaty of Alliance signed on February 6, 1778. France recognized the United States as an independent nation and agreed to cooperate militarily against Great Britain.
French support included troops, naval forces, weapons, money, and supplies. French naval power was especially important in the Yorktown campaign, where the French fleet helped prevent a British evacuation or reinforcement by sea. The combined American and French victory at Yorktown in 1781 effectively ended major fighting.
France’s involvement grew from rivalry with Britain as well as sympathy for the American cause. The alliance was not simply a cultural friendship, and France’s financial and military commitment placed heavy pressure on its own treasury. The war’s costs contributed to the broader crisis that preceded the French Revolution.