Among the Twelve Deceptive Stratagems recorded in The Art of War · Initial Estimations, Sun Tzu put forward a lethal psychological warfare tactic: Divide the united enemy (親而離之).
In the chaotic aftermath of Yuan Shao’s death in 202 CE, his sons Yuan Tan and Yuan Shang turned from heirs into enemies, igniting a civil war that would seal the fate of northern China.