The Battle of Yorktown, more precisely the Siege of Yorktown, forced the British army under Charles Cornwallis to surrender in 1781.
American and French forces surrounded Yorktown, Virginia, in September and October 1781. George Washington commanded the combined American and French army, while French naval forces helped prevent a British relief fleet from breaking the blockade. The allies gradually tightened their lines and captured key defensive positions.
Cornwallis surrendered on October 19, 1781. The victory did not instantly end every military operation, but it was the last major land battle of the Revolutionary War. British political support for continuing the conflict weakened sharply afterward, leading to peace negotiations.
The conflict formally ended with the 1783 Treaty of Paris. Yorktown is therefore best understood as the decisive military victory that made the peace settlement possible, rather than the legal document that ended the war.