In the late summer of 1777, General Howe loaded his army on transports and moved by sea to the Chesapeake Bay, where they landed with the intent of taking the American capital of Philadelphia from the south. Washington rushed his troops south to defend the invasion, and the focus of major conflict shifted from the vicinity of New York to the vicinity of Philadelphia. In Pennsylvania, the Americans suffered defeats at Brandywine in September and at Germantown in October.
West of Philadelphia, in New Jersey, this shift played out in the concentration of military action along the Lower Delaware River, from Gloucester to Bordentown. American action focused upon preventing the British from controlling the approach to Philadelphia up the Delaware, through which they could supply their army once they took the capital. The Battle of Red Bank ensued, and the British carried the day.
The Americans would retreat to Valley Forge, where they would regroup and train for the future. And in February 1778 they would learn that the French had joined the war as an American ally.