After the French and Indian War, the British controlled a large portion of the Trans-Appalachian frontier. In 1763, they forbid the settlement of lands west of the Appalachian Mountains. From their posts north of the Ohio River they began sending Indian war parties against settlers who ignored the proclamation line.
In an attempt to stop the raids, George Rogers Clark led his Kentucky militia and frontiersmen into Illinois territory to strike at the base of Indian operations. There, he captured two British posts along the Mississippi, then turned his small army toward Vincennes.
After an 18-day trek through the dead of winter, Clark and his force of 170 Americans and Frenchmen reached Fort Sackville, arriving on February 23, 1779. After spending February 24 re-supplying, thanks to French citizens of Vincennes, Clark managed to convince the larger British garrison that he had an even larger force.
Clark’s men surrounded the fort and paraded flags sufficient for an army of 500 men. His frontiersmen also maintained such a rapid rate of fire that the British thought there were a large number of Americans. He next ordered tunneling operations to convince the British that he was tunneling to place explosives under the fort walls. Further, he ordered five captured Indians to be tomahawked in full view of the fort in order to un-nerve the defenders.
On February 25, the defeated British army surrendered Fort Sackville.