Final answer:
The British were forced to surrender at Yorktown due to the help of French troops and a French Fleet, Washington's victories in the field, and the British commander's underestimation of Washington's army.
Step-by-step explanation:
The British were forced to surrender at Yorktown because French troops and a French Fleet helped trap the British, which prevented them from receiving reinforcements or supplies. Additionally, Washington was able to defeat the British in the field during the Siege of Yorktown. The British commander, General Charles Cornwallis, also underestimated the size of Washington's army, which further weakened their position.
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