On September 11, 1777, General Sir William Howe and General Charles Cornwallis launch a full-scale British attack on General George Washington and the Patriot outpost at Brandywine Creek near Chadds Ford, in Delaware County, Pennsylvania, on the road linking Baltimore and Philadelphia.

Howe and Cornwallis spilt their 18,000 British troops into two separate divisions, with Howe leading an attack from the front and Cornwallis circling around and attacking from the right flank. The morning had provided the British troops with cover from a dense fog, so Washington was unaware the British had split into two divisions and was caught off guard by the oncoming British attack.

Although the Americans were able to slow the advancing British, they were soon faced with the possibility of being surrounded. Surprised and outnumbered by the 18,000 British troops to his 11,000 Continentals, Washington ordered his men to abandon their posts and retreat. Defeated, the Continental Army marched north and camped at Germantown, Pennsylvania. The British abandoned their pursuit of the Continentals and instead began the British occupation of Philadelphia. Congress, which had been meeting in Philadelphia, fled first to Lancaster, then to York, Pennsylvania, and the British took control of the city without Patriot opposition.

The one-day battle at Brandywine cost the Americans more than 1,100 men killed or captured while the British lost approximately 600 men killed or injured. To make matters worse, the Patriots were also forced to abandon most of their cannon to the British victors after their artillery horses fell in battle.