Howe had been assured that loyalists predominated in Pennsylvania, and he hoped they would help him acquire fresh supplies and horses for his army. What he found was disillusioning. Most of the population fled from an army whose conduct in New Jersey had been publicized in lurid colors. Militia drove off herds and burned fields and granaries. As he slowly made his way toward Philadelphia, Howe knew that he was traversing a hostile countryside.

With Howe operating from the Chesapeake, Washington was confident that Burgoyne could accomplish nothing of significance in the north. Washington felt free to leave the immediate environs of New York and moved his army south to defend Philadelphia. Congress and public opinion expected Washington to defend the capital of the United States, but he himself was more than ready to engage the British again. His army paraded through Philadelphia on its way to meet the British. John Adams watched the troops march by and wrote Abigail that he was not impressed with their military bearing. “They don't step exactly in time. They don't hold up their heads quite erect, nor turn out their toes exactly as they ought. They don't all of them cock their hats, and such as do, don't all wear them the same way.” A military observer noted that they were “indifferently dressed” but thought they looked “as if they might have faced an equal number with a reasonable prospect of success.”

Riding with Washington through the streets was the Marquis de Lafayette, a twenty-year-old French aristocrat who had crossed the Atlantic to offer his services to the new American republic. Congress had initially been cool to the youngster when he appeared and asked to be made a major general. The members of Congress were getting tired of the European adventurers who made their way to America, expecting appointment to high rank in the Continental army. Lafayette's sincere sympathy for the American cause and his willingness to serve without pay softened the legislators. So too did his relative modesty; he wanted only to be “near the person of George Washington till such time as he may think proper to entrust me with a division of the army.” Lafayette received his rank and a secure place in Washington's military “family.”

Washington stationed his army along Brandywine Creek south of Philadelphia. He had 8,000 Continentals and 3,000 militia with him. On September 10, Howe's army entered nearby Kennett Square. Washington expected a frontal assault, probably at one of the fords across the rugged Brandywine. Sullivan commanded his right. Greene commanded the center of the line. The left was entrusted to the militia because the terrain there made an attack unlikely. Almost inexplicably, Washington made no provision for the sort of flanking attack that Howe had used to such effect the previous year.

Howe remained true to form. He left a force under General Baron Wilhelm von Knyphausen to occupy Washington's attention while he took the rest of the army on a long march around the Americans' right flank. Contradictory reports about this began to reach Washington in the morning and early afternoon of September 11. At one point he contemplated launching his whole army forward to catch what he thought was the rear of the British army. In the end he stayed put too long. Howe appeared in Sullivan's rear; Sullivan tried to form a new line to resist this unexpected attack, but his men were routed and fled.

Washington sent Greene with his reserves to block Howe, leaving Anthony Wayne to hold Chad's Ford against Knyphausen. Greene's men marched four miles in forty-five minutes. Running into the advancing British, they fought a holding action, covering the retreat of Sullivan's troops. Then they made a disciplined withdrawal, keeping the pursuing British at bay. Knyphausen attacked the weakened American center and forced it back. By nightfall the American army had been driven from the field. Washington had suffered more than 1,000 casualties; Howe something over half that number.