Final answer:
The British Army, led by Lord Charles Cornwallis, was on the losing side in the Battle of Yorktown, leading to the end of the American Revolution and the Treaty of Paris.
Step-by-step explanation:
The Battle of Yorktown
The military force on the losing side in the Battle of Yorktown was the British Army. Commanded by Lieutenant General Lord Charles Cornwallis, the British forces were defeated by the combined American and French armies under the command of General George Washington. Cornwallis's army was besieged in Yorktown, Virginia, and after a failed breakout attempt, he was forced to surrender on October 19, 1781. This event marked the end of the American Revolution and led to peace negotiations that culminated in the Treaty of Paris, officially recognizing American independence.