He knew, as the enemy had little idea, just how big a country it was.

From 1776 by David McCulough. Page 249.  Washington retreating through New Jersey, considering his strategic options.

Washington worried about the health of his men. He worried about rumors of a British invasion to the south of Newark at Perth Amboy, at the mouth of the Raritan River, where New Jersey and Staten Island were separated by only a narrow channel.

In less than two weeks, on December 1, the enlistments of 2,000 of his troops would be up, the men free to go. It was the same nightmare prospect he had faced at Boston exactly a year before, and with the misery of the men greater now than ever, and morale suffering, there seemed every chance that his army would evaporate before his eyes.

Privately, Washington talked with Reed about the possibility of retreating to western Pennsylvania if necessary. Reed thought that if eastern Pennsylvania were to give up, the rest of the state would follow. Washington is said to have passed his hand over his throat and remarked, “My neck does not feel as though it was made for a halter.” He talked of retreating to the mountains of Augusta County, in western Virginia. From there they could carry on a “predatory war,” Washington said. “And if over-powered, we must cross the Allegheny Mountains.”  He knew, as the enemy had little idea, just how big a country it was.

The problem was not that there were too few American soldiers in the thirteen states. There were plenty, but the states were reluctant to send the troops they had to help fight the war, preferring to keep them close to home, and especially as the war was not going well. In August, Washington had had an army of 20,000. In the three months since, he had lost four battles—at Brooklyn, Kips Bay, White Plains, and Fort Washington—then gave up Fort Lee without a fight. His army now was divided as it had not been in August and, just as young Lieutenant Monroe had speculated, he had only about 3,500 troops under his personal command—that was all.