What was one factor that caused the British to surrender at Yorktown?

The French and American forces joined together to block the British from getting supplies.

Explanation:

The French navy fought to keep the British Navy from helping the army, and the armies of the US and French surrounded, cut off, and then slowly defeated the British forces, forcing them to surrender. And because the British navy couldn't show up to help the British army, the Brits surrendered.

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