Which 1777 battle persuaded France to formally ally with the American revolutionary cause?

The Battle of Saratoga persuaded France to formally ally with the American revolutionary cause.

The Battles of Saratoga took place in New York in September and October 1777. American forces under General Horatio Gates defeated a British army commanded by General John Burgoyne, who surrendered at Saratoga on October 17.

The victory demonstrated that the Continental Army could defeat a major British force. France had already provided covert assistance, including supplies and weapons, but Saratoga encouraged King Louis XVI’s government to recognize the United States and sign the Treaty of Alliance in 1778.

French military and financial support became crucial to the American war effort. French troops and naval forces later worked with George Washington’s army at Yorktown, where the British surrendered in 1781. Saratoga is often called a turning point, though the war continued for several more years after the victory.