Charleston harbour in 1817

That winter Clinton and Cornwallis went south.  The British had held Savannah, Georgia, since December 1778 and had fought back an American and French invasion in October 1779.  Now the British wanted Charleston, South Carolina.  With control of the major coastal cities, the British could use their sea power to move troops from point to point.   And it was believed that there were many people in the Carolinas still loyal to the crown who would join with their British liberators to bring the war to an end. 

Charleston fell to the British in May 1780.  Clinton returned to New York and Cornwallis moved into the interior of South Carolina and crushed General Horatio Gates at Camden in August 1780.  Gates had been the general who gave the British their first major defeat at Saratoga, New York, in October 1777.