Preserving the Army was more vital than holding ground
In December 1776 Thomas Paine reflected on the year past and wrote, "These are the times that try men's souls." No American who lived through 1776 doubted the truthfulness of Paine's lament, and no one had had his soul more tried than the commander in chief of the Continental Army, George Washington.
At the order of the Continental Congress in June 1775 Washington had taken command of an assemblage of men (not yet an army) that had gathered in the days following Lexington and Concord and were laying siege to the British force occupying Boston.
Over the next eight months Washington turned this rabble under arms into a recognizable force - the Continental Army. He and his army worked to tighten the noose on the enemy until finally in March 1776 the British commander, Gen. William Howe, ordered an evacuation.
The British retreated to Halifax, Nova Scotia, where they regrouped and planned an attack on New York City. Washington got to New York first, where he set to work immediately preparing defenses.
The decision to stand at New York was a political necessity but a tactical mistake.
New York's support for the American cause was essential. To have abandoned the city would have resulted in disastrous political consequences.
Militarily, however, it was impossible for Washington to win. Control of the city, bordered on three sides by water, rested on naval power. Washington had none, while General Howe could rely upon his brother, Adm. Lord Richard Howe, to deliver the world's mightiest fleet.
Washington's tactical disadvantages were compounded by his own errors. Splitting his force between Manhattan and Long Island nearly cost him his army, and his later decision to hold Fort Washington led to disaster.
Had General Howe been a more imaginative and aggressive commander the British might have "bagged the fox" in New York. That they did not, however, was not due to incompetence or lethargy, but rather, as David McCullough rightly points out in "1776," to the British command's adherence to 18th-century tactical doctrine. Howe did what he was expected to do and he did it well.