Charles Cornwallis commanded the British forces besieged at Yorktown in 1781.
Cornwallis moved his army into Yorktown, Virginia, a position on the York River, expecting support from the Royal Navy and other British forces. Instead, the French fleet defeated or blocked the expected naval relief in the Battle of the Chesapeake, leaving his army increasingly isolated.
American forces under George Washington and French forces under the Comte de Rochambeau surrounded Yorktown. Their siege lines, artillery, and control of the Chesapeake approaches placed intense pressure on Cornwallis's army. On October 19, 1781, the British force capitulated, effectively ending major fighting in the Revolutionary War.
Cornwallis did not personally attend the formal surrender ceremony; General Charles O'Hara represented him. That detail is why “Cornwallis surrendered at Yorktown” is common shorthand but technically imprecise. The Treaty of Paris, signed in 1783, formally ended the war and recognized American independence.