The Battle of Brandywine was one of several hard losses for the Americans. It was disheartening to the Patriots, though events did eventually turn in their favor.
In September of 1777, General George Washington was stationed in Philadelphia with the continental army. Washington was aware of the oncoming British army led by General William Howe. In preparation for their arrival, he stationed troops along the Brandywine River to guard the main fords. He was hoping to force the British to Chadds Ford, where most of his army was stationed and he’d have the advantage. However, Howe formulated a better plan. He had his army sail up river a little farther, cross at a ford there, march down south, and attack the Americans from the rear.
On September 11, 1777 there was a thick fog covering the ground. This allowed the British troops to move undetected. Washington was still under the impression that Howe would send his entire force to attack at Chadds Ford. When Howe crossed the river, he gained a strategic advantage near Birmingham Friends Meeting House.
The fog allowed Howe to get his entire army across the river by noon, and by the time Washington realized his mistake, the British had appeared on their right flank. In a panic, he ordered his men to take the high ground near Birmingham Friends Meeting House. However, in the confusion between the surprise attack and the change in orders, the Americans did not properly defend their positions.
They fought the Battle of Brandywine all day long, however the Americans were clearly outwitted and confused as to their orders. When night fell, the battle ended, and the Americans retreated to Chester. Most of the army arrived at Chester by midnight, however soldiers were still making their way in until dawn.
Due to the loss, the Americans were forced to surrender Brandywine to General Howe. In the next few weeks, Washington and Howe both tried to maneuver their armies toward Philadelphia (the capital at that time). As they grew closer it became clear that the British would take Philadelphia, so Congress fled the city, and thus George Washington lost Philadelphia to the British.