When the Continental Congress signed the Declaration of Independence on 4 July 1776, the Commander-in-Chief of the American armies, General George Washington, was in New York, fully aware of the impending arrival of a great armada of British ships. Admiral Richard Howe commanded the fleet of two dozen warships and several hundred supply ships; his younger brother, General William Howe, headed the army of 32,000 British and German troops. About two weeks after the signing of the Declaration of Independence, the ships arrived in New York Harbor. The army landed and established a huge base of operations on Staten Island (perhaps understandably, the 18th-century British installation on Staten Island does not appear to be part of the historical interpretation offered by the Fort Wadsworth Visitor Center at the Gateway National Recreation Area).

General Howe initiated the New York Campaign quickly and met with immediate success. On 22 August Howe landed nearly half his army at Gravesend, the southwestern corner of Long Island, now part of the Borough of Brooklyn. The Continental Army prepared two lines of defense, the first along a long ridge of hills which ran from Bay Ridge in the southwest to Jamaica Pass in the east and was known as Long Island Heights. The second was a series of fortifications on the eastern slopes of Brooklyn Heights. The British appeared to prepare for engagement at three locations, at Gowanus Bay on the west, Flatbush Pass in the center, and Bedford Pass in the eastern section of Washington Heights.

It was under the cover of darkness, however, at 1 a.m. on 27 August, that the Battle of Brooklyn began to unfold. At that time, General Howe ordered the main body of British troops, under the command of Generals Clinton and Cornwallis, to march several miles east, all the way to Jamaica Pass. Arriving before dawn, the British captured the few American sentries, secured the pass, and thereby outflanked all the American positions along Washington Heights. By 7 a.m. the British were marching west and appearing behind the American forces at both the Bedford and Flatbush passes. At 9 a.m. the British and Hessian forces positioned to the south of the Heights began their attack. By noon the Americans had retreated to Brooklyn Heights.

Much of the heaviest fighting had taken place in what is now New York City's 500-acre Prospect Park and the nearby J.J. Byrne Park in Park Slope, where the Battle is commemorated at the rebuilt Old Stone House (the Vechte-Cortelyou House). Washington realized he could not defend Fort Greene and the other fortifications at Brooklyn Heights and on 30 August he withdrew all American forces to New York City, then a mile-square town concentrated in the southernmost end of Manhattan.

General Howe next deployed his army for an invasion of Manhattan. On 15 September the British crossed the East River and expelled the Americans from New York City, driving them north through Manhattan all the way to Harlem Heights. A day later, however, from a vantage point at "The Point of Rocks" (the site is incorporated into present day Saint Nicholas Park), Washington successfully directed the Continental Army in the Battle of Harlem Heights. The Americans defended their advantageous position and forced the British to devise another means for pushing Washington's troops off the island.

As the British were settling into New York City, a fire broke out on 21 September and then raged throughout the day, burning a large portion of the city to the ground. The Patriot army having withdrawn, New York's Tories dispensed vigilante-like "justice" against any person suspected of having American sympathies. Gangs of men and mob violence filled the streets. The British captured 24-year-old Nathan Hale, accused him of spying for the Continental Army, and hanged him, but not before he spoke the words which made him the first American hero of the War, "I only regret that I have but one life to lose for my country."

Able to return his attention to the military Campaign, General Howe, on 12 October, ordered a flanking motion, using the British naval force to transport troops and supplies up the East River and land them at Throgs Neck. The army then marched inland and encamped at New Rochelle. Washington, recognizing the ability of the British to attack his position from the south and the east simultaneously, decided to vacate Harlem Heights. On 16 October he began the withdrawal of American forces to Westchester County, New York, leaving behind a large garrison at Fort Washington, at the far northwest corner of Manhattan and a somewhat smaller force at Fort Lee, across the Hudson River in New Jersey.

The Continental Army marched to White Plains, New York and encamped. The British soon pursued from New Rochelle and attacked. On 28 October the two armies meet in the Battle of White Plains. The British were victorious again, driving the Americans out of the town and scattering them in the countryside around North Castle. Washington had made his headquarters in the Miller farm house, now a historic house museum. Miller Hill, which played a small part at the close of the Battle of White Plains, has been preserved and may be toured from the historic house museum.

General Howe, believing that Washington would not regroup his army for another major engagement with the British, turned his attention to the two Hudson River forts in his rear. Taking two weeks to prepare, the British forces attacked Fort Washington on 16 November and took it that same day (the site of the Fort is incorporated in present day Bennett Park); it was a huge loss for the Patriot cause, as 2,700 American soldiers surrendered. General Howe then looked across the Hudson River to Fort Lee. The Continental Army, having crossed the Hudson at Peekskill, was marching south along the Hackensack River. The British wasted no time.