Guo Tu
In the autumn of 202, Cao Cao waged war against the Yuans' ally Liu Biao to his south, part of a strategy to let the Yuan brothers tire themselves out. Taking advantage of Cao Cao's apparent absence, Yuan Shang marched his men to Nanpi and defeated Yuan Tan there. Yuan Tan fled south into Qing province, to Pingyuan. Though it was Yuan Tan's former domain, Qing province had been slowly encroached by Cao Cao's general Zang Ba. So when Yuan Shang followed up his attack by laying siege to Pingyuan, Yuan Tan could not expect much help within his province. Yuan Tan's key advisor Guo Tu summarized the situation and proposed an unlikely alliance: