The British successfully implemented the first part of their strategy to isolate New England when they took New York City in the fall of 1776. For the next seven years, they used New York as a base of operations, expanding their control to Philadelphia in the winter of 1777. After suffering through a terrible winter in 1777–1778 in Valley Forge, Pennsylvania, American forces were revived with help from Baron von Steuben, a Prussian military officer who helped transform the Continental Army into a professional fighting force. The effort to cut off New England from the rest of the colonies failed with the General Burgoyne’s surrender at Saratoga in October 1777. After Saratoga, the struggle for independence gained a powerful ally when France agreed to recognize the United States as a new nation and began to send much-needed military support. The entrance of France—Britain’s archrival in the contest of global empire—into the American fight helped to turn the tide of the war in favor of the revolutionaries.