c) A hurricane

An unexpected and crucial event that significantly influenced the American victory at the Battle of Yorktown was a hurricane. In 1781, as the American and French forces prepared to confront the British at Yorktown, a powerful hurricane struck. This natural disaster disrupted the British fleet, hindering their ability to provide support and reinforcements to the troops led by General Cornwallis. The storm’s timing proved advantageous for the American and French forces, as it allowed them to fortify their positions and complete the encirclement of Yorktown. This fortuitous turn of events played a key role in the eventual American victory, a decisive moment in the Revolutionary War.