1781
Siege of Yorktown
The setting
Yorktown, Virginia
Tidewater peninsula between the York and James rivers; British earthwork fortifications
Reveal the outcome
Recorded sideGreat Britain
Recorded resultTrapped and forced to surrender the army
British army surrenders; effective end of major combat operations
How the atlas explains it
Admiral de Grasse's French fleet defeated the Royal Navy at the Battle of the Chesapeake (5 Sept 1781), sealing the bay and denying Cornwallis any seaborne rescue or escape. Spanish support was pivotal indirectly: Bernardo de Galvez's Gulf campaign tied down British forces, and Spanish funds raised in Havana helped finance de Grasse's fleet. With the sea closed, a textbook Franco-American siege reduced the British works.
What followed
The loss of a second British field army broke London's will to continue the war and led directly to peace negotiations and American independence.