Louis XVI was the French monarch who allied with the United States during the American Revolution in 1778.
France formally joined the American cause through the Treaty of Alliance and the Treaty of Amity and Commerce, signed in February 1778. Louis XVI’s government recognized the United States and agreed to cooperate against Great Britain, while the American side promised not to make a separate peace without French agreement.
French support was decisive because it supplied soldiers, weapons, money, military advisers, and naval forces. French naval action helped prevent British relief at Yorktown in 1781, where General Charles Cornwallis surrendered to American and French forces under George Washington and Rochambeau.
Louis XVI was a Bourbon king who reigned from 1774 until 1792. He was later executed during the French Revolution in 1793. Louis XIV and Louis XV were earlier Bourbon kings, while Charles X ruled France after the revolutionary and Napoleonic periods.