Cornwallis returned to New York, and Washington occupied Princeton. In September 1777, Cornwallis led three thousand troops into Philadelphia, taking the city without firing a shot. However, the decisions and subsequent events that brought Cornwallis to Philadelphia contributed to the defeat of General John Burgoyne at Saratoga, New York. Burgoyne's surrender was a major turning point of the war in favor of the colonies, as it secured foreign assistance for the colonial war effort. .
In 1779, Cornwallis, promoted to Lieutenant General, became second in command to Sir Henry Clinton. Given a dormant commission, he was to succeed Clinton in the event of Clinton's death or resignation. In August 1779, Clinton requested to resign, recommending Cornwallis. Clinton's request made the dormant commission all the more significant, but it was not to be, as Clinton remained in command. They met again at Charleston, Virginia in February 1780, where Cornwallis consulted on every decision. Clinton's proclivity to procrastinate, combined with the indeterminate state of Clinton's resignation, became a source of irritation between the two. Clinton thought that Cornwallis committed a colossal error in judgment, and missed a superb chance to annihilate the Continental Army at Trenton. Clinton also thought that Cornwallis was scheming for an independent command. Despite the acrimony that developed between them, Cornwallis assisted Clinton in the capture of Charleston. When Clinton returned to New York, Cornwallis assumed command of the southern campaign and set out to secure South Carolina. .
Following his success at Charleston, he achieved another victory at Camden, defeating General Horatio Gates, the general who defeated Burgoyne at Saratoga. Cornwallis knew he was outnumbered, and that militia composed a large portion of the opposing army. Cornwallis believed that British regulars had superior training and discipline, a belief shared among British military leadership that made them confident of eventual victory in America.
