Which American Revolutionary War battles helped persuade France to formally ally with the United States?

The Battles of Saratoga helped persuade France to formally ally with the United States during the American Revolutionary War.

The campaign took place in 1777 in upstate New York. British General John Burgoyne led an army south from Canada, aiming to divide New England from the other colonies by controlling the Hudson River Valley. American forces eventually stopped and surrounded his army.

Burgoyne surrendered at Saratoga on October 17, 1777. The victory demonstrated that the American forces could defeat a major British army, changing European assessments of the war. France had already been secretly supplying the Americans, but the American success encouraged it to enter an open alliance.

The resulting Franco-American Alliance was signed in 1778. French military, naval, financial, and material support became crucial to the American war effort and helped move the conflict onto a global stage. Saratoga is sometimes described as a single battle, but the name usually refers to the two principal engagements and the wider campaign.