The Strategy of Sowing Discord
Undermine your enemy's ability to fight by secretly causing discord between him and his friends, allies, advisors, family, commanders, soldiers, and population. While he is preoccupied settling internal disputes his ability to attack or defend, is compromised.
Six Dynasties Period China
In the later Wei dynasty, the emperor Tai Wu led a hundred thousand troops against the Song general Zang Zhi. The emperor, with his superior forces, chased general Zhang to the city of Yu where he was cornered. The city was strongly fortified and so the emperor planned to surround it and starve the defenders into surrender. Feeling confident of his position, the emperor sent a cart carrying a large jar of wine to the city gate with the message asking for the traditional exchange of wine before commencing his siege of the city. Zang Zhi knew that he needed to fight a decisive battle quickly, or suffer defeat, saw this as an opportunity. He sent some soldiers to gratefully accept the jar of wine and in turn deliver another large jar sealed with the wine maker's stamp. When a cup of this wine was poured for the emperor it was discovered to be urine. This caused the emperor a humiliating loss of face before his own troops and in a rage ordered an immediate assault on the city. The defenders were well prepared and the bodies of the slain imperial troops piled up nearly to the top of the ramparts. In his haste and anger the emperor lost half his forces.