They will be submit to you on their own." Cao Cao ignored Jia Xu and proceeded to attack Jiangdong. He lost the decisive Battle of Red Cliffs against the allied forces of Sun Quan and Liu Bei later that year. Pei Songzhi, who annotated Jia Xu's biography in the "Sanguozhi", argued that Jia Xu's advice to Cao Cao was inappropriate. He pointed out that Cao Cao's territories lacked the stability necessary for Cao Cao to do as Jia Xu advised – focus on economic development in Jing Province. Moreover, Cao Cao had to deal with the external threats posed by warlords such as Han Sui and Ma Chao in the northwest. Pei Songzhi noted that Jing Province was highly unstable and would not remain under Cao Cao's control for long, because of the polarising effects of the presences of Liu Bei and Sun Quan in the region. He pointed out that during the Battle of Jiangling in 208, Cao Cao's general Cao Ren still lost Jiangling Commandery to Sun Quan and Liu Bei's forces despite his best efforts at defending it. Pei Songzhi thus concluded that it was impossible for Cao Cao to focus on economic development in Jing Province, given how unstable the region was, therefore Jia Xu's advice was inappropriate. He argued that Cao Cao made a right choice to attack Jiangdong at the right time, when he had resources for naval warfare acquired from his recent annexation of Jing Province. He also mentioned that Cao Cao's defeat at the Battle of Red Cliffs was not due to miscalculation or poor planning, but because of uncontrollable factors such as the plague which affected his troops and the winds which fanned the fire that destroyed his naval fleet. In 211, Cao Cao engaged a coalition of northwestern warlords led by Han Sui and Ma Chao at the Battle of Tong Pass. Ma Chao and others agreed to make peace with Cao Cao on two conditions. Firstly, Cao Cao had to give up the northwestern territories to them. Secondly, Cao Cao had to grant them official titles. Jia Xu suggested that Cao Cao pretend to agree to their terms, and then try to sow discord among them. Cao Cao heeded Jia Xu's advice. When internal conflict broke out between Han Sui and Ma Chao, Cao Cao took advantage of the situation to attack them and achieved victory. Sometime between 211 and 217, a power struggle broke out between two of Cao Cao's sons over the succession to the "King of Wei" (魏王), the nominal vassal king title held by their father.