Wei were killed, and Cao Cao himself narrowly escaped from death. On the advice of Jia Xu, Zhang Xiu eventually surrendered to Cao Cao in the winter of 199–200. In addition, in 197, Cao Cao was able to persuade Ma Teng and Han Sui, who controlled Yong and Liang provinces (covering most of present-day Shaanxi and Gansu), to submit to him. That year, Yuan Shu declared himself "Son of Heaven" in Shouchun (壽春; present-day Shou County, Anhui), an act perceived as treason against the Han dynasty government, prompting other warlords to use that as an excuse to attack him (see Campaign against Yuan Shu). Sun Ce, son of Sun Jian, who had conquered several territories in Jiangdong between 194 and 199, ended his alliance with Yuan Shu and became an independent warlord. Lü Bu, who was also previously Yuan Shu's ally, broke ties with Yuan and dealt him a major defeat near Shouchun. Cao Cao also attacked Yuan Shu and defeated him. Yuan Shu attempted to flee north to join Yuan Shao but his way was blocked and he would die of illness on his return to Shouchun in 199. In 198, Yuan Shao tried to persuade Cao Cao to move the capital to Juancheng (鄄城; in present-day Heze, Shandong), which was nearer to his own territory, in an attempt to wrestle Emperor Xian away from Cao, but Cao refused. Later that year, Cao Cao joined forces with Liu Bei to attack Lü Bu, defeating him at the Battle of Xiapi. Lü Bu was captured and executed on Cao Cao's order, and Xu Province came under Cao's control. In 199, Gongsun Zan was defeated by Yuan Shao at the Battle of Yijing and he committed suicide by setting himself on fire. Gongsun Zan's territories, which extended to the northern boundaries of the Han dynasty's empire, were completely annexed by Yuan Shao. Yuan Shao then turned his attention south towards Cao Cao, who was an emerging power in central China. Yuan allied with Liu Biao and was intent on attacking Cao Cao. Guandu campaign (200–201) Against the advice of Ju Shou and Tian Feng, who reasoned that their troops were exhausted after the battles against Gongsun Zan and needed rest, Yuan Shao prepared for a campaign against Cao Cao, confident that his much larger army could easily crush Cao Cao's. While Cao Cao readied himself for battle, he discovered that Dong