At about the time Benedict Arnold was negotiating a deal to harm the American cause in the North, British victories were demoralizing the South. Momentum in favor of the patriots had gone downhill since their decisive win at Sullivan's Island early in the war (1776).
Even huge American successes (like the battle of Saratoga where General Burgoyne and his Redcoats were routed and European powers - like France - began to believe it was smart to support the colonies) did not change the British belief that they could hold the South.
To make matters worse, Southern families were divided. Loyalist fathers were pitted against patriot sons while brothers and cousins fought against each other. Charleston, once the fourth largest (and richest) city of the colonies was besieged and fell to the British in May, 1780.
But just as soon as the British and their young victorious general, Banastre Tarleton, were confident they would hold their southern prize, a South Carolina patriot forever changed the momentum of war in the South. Francis Marion and his troop of 150 men ("Marion's Brigade) would soon chase the Redcoats out of South Carolina, setting up the final British defeat at Yorktown.
Not bothered by his lack of men and supplies, Marion brilliantly used a weapon unknown to the British: the swamps, waterways and marshes of the South Carolina low country. Employing guerilla tactics to harass the enemy, Marion and his men would strike without warning and then disappear into the swamps.
Tarleton, previously feared by southerners for his brutal and bloody attacks, was exasperated when his communications were interrupted, his supply lines were cut off, and his hold on the south slipped away. Powerless to stop the constant unconventional attacks,
The British soldier trembles
When Marion's name is told.
The Redcoats could not capture Francis Marion. He and his men were never defeated. Tarleton called him the "swamp fox." (The Patriot calls him Benjamin Martin - played by Mel Gibson.)