Final answer:
New York was under British control starting in 1776 as they aimed to isolate and defeat the insurgents in New England, which ultimately failed with their defeat at the Battle of Saratoga.
Step-by-step explanation:
On September 17, 1776, New York was under British control. After abandoning Boston, British forces concentrated on capturing key colonial cities to isolate New England and quell the burgeoning rebellion. They started with New York City in 1776, which they captured with relative ease. The subsequent year saw the British capture of Philadelphia, the American capital at the time. However, the larger strategy to isolate New England did not succeed, demonstrated by the British defeat at the Battle of Saratoga in the fall of 1777, which was a turning point in the American Revolutionary War. New York City served as the primary base for British operations for the duration of the war.