France became the decisive formal ally of the American colonies during the Revolutionary War.
France signed the Treaty of Alliance with the United States in 1778, after the American victory at Saratoga demonstrated that the rebellion could succeed. The alliance brought military aid, loans, supplies, troops, and naval support to the American cause.
French forces played a crucial role in the 1781 Yorktown campaign. French soldiers under the Comte de Rochambeau joined Washington’s army, while the French navy helped prevent British reinforcement and escape by sea. Lord Cornwallis surrendered at Yorktown, effectively ending major combat.
France’s intervention was motivated partly by its rivalry with Great Britain and its desire to recover influence after the Seven Years’ War. Spain and the Dutch Republic also opposed Britain in the wider conflict, but France was the principal formal ally of the American revolutionaries.