Battle of Saratoga
On 17th Oct. 1777, British General Burgoyne surrendered to American General Horatio Gates after two battles that took place near Saratoga, New York. This was the first major victory for an army of American volunteers against all mighty England and their professional armies.
While this battle did not stop the war, once the news reached Benjamin Franklin in Paris (who had come as commissioner seeking help from France), it gave his case a lot more weight.
And less than three months later, Franklin was able to convince the Count de Vergennes, foreign affair minister, who in turn convinced King Louis XVI to support the American cause...