What important location did Washington lose to the British during the Revolutionary War as noted in the biography, Washington: A Life?

New York was an important strategically location during the Revolutionary War that Washington regretfully lost to British control. However, when the British surrendered, Washington entered New York amid much fanfare. Years later, Washington would take the oath of office in New York and serve as president there until the capital was moved to Philadelphia for ten years in anticipation of the creation of a new capital in the Potomac Valley.