Cao Cao's roughly 20,000 troops broke Yuan Shao's 100,000+ army near Guandu (modern north Henan, close to Xuchang) by torching the Wuchao supply depot on intelligence from the defector Xu You (
许攸). Together with Fei River and Red Cliffs, it is one of the classic
以少胜多 ('fewer defeating many') battles of Chinese military history.
