history
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.