The Siege of Yorktown or Battle of Yorktown in 1781 was a decisive victory by combined assault of American forces led by General George Washington and French forces led by General Comte de Rochambeau over a British Army commanded by Lieutenant General Lord Cornwallis. It proved to be the last major land battle of the American Revolutionary War, as the surrender of Cornwallis's army prompted the British government eventually to negotiate an end to the conflict.

In 1780, 5,500 French soldiers landed in Rhode Island to try to help their American allies in assaulting British-controlled New York City. The two armies met North of New York City in 1781. The French Commander, the Comte de Rochambeau, convinced the American Commander, George Washington, that an attack on New York City would be hard pressed to succeed and it would be easier for the French Fleet under the command of the Comte de Grasse to assist in the attack further south, because he was to bring the French Fleet into the Caribbean in October. Thus, they agreed to attack Lord Cornwallis and his smaller army of 9,000 men stationed in the port town of Yorktown, Virginia. In the beginning of September, de Grasse defeated a British fleet led by Admiral Hood that came to relieve Cornwallis at the Battle of the Chesapeake. As a result of this victory, de Grasse blocked any escape by sea for Cornwallis. Washington dispatched the French general Marquis de Lafayette to contain Cornwallis in Yorktown until he arrived, and Lafayette did so. By late September the army and naval forces surrounded Cornwallis by land and sea.

After initial preparations, the Americans and French built their first parallel and began the bombardment. With the British defense weakened, Washington, on October 14, 1781, sent two columns to attack the last major remaining British outer defenses; redoubts #9 and #10. A French column took #9 and an American column #10. With these defenses gone, the allies were able to finish their 2nd parallel. With the Americans' artillery closer and more intense than ever, the British situation began to deteriorate rapidly and Cornwallis asked for capitulation terms on the 17th. After two days of negotiation, the surrender ceremony took place on the 19th, with Cornwallis being absent since he claimed to be ill. With the capture of over 8,000 British soldiers, negotiations between the United States and Great Britain began, resulting in the Treaty of Paris in 1783.

en.wikipedia.org/wiki/Siege_of_Yorktown