the emperor back to his base in Xu (許; present-day Xuchang, Henan), establishing the new capital there. From then on, although Cao Cao was a subject of Emperor Xian in name, he actually wielded state power and controlled the imperial court. Despite so, Cao Cao never showed disrespect to Emperor Xian, and instead, honoured the emperor according to formal imperial protocol. Cao Cao also issued imperial edicts in Emperor Xian's name to other warlords, ordering them to submit to imperial authority when in fact they were actually submitting to him. When Cao Cao sent Yuan Shao an edict in the emperor's name, only then did Yuan realize that he had lost an opportunity to make use of the emperor to control other warlords. Cao Cao's rise to power (196–199) Even after moving to the new capital at Xu, the central government still lacked funds and food supplies. As suggested by Zao Zhi (棗祇), Cao Cao implemented a new tuntian policy to promote agricultural production, in which soldiers were sent to grow crops, and the harvest would be shared between the military and civilian population. The policy yielded commendable results as the area around Xu developed into highly productive farmland and the problem of shortage of food was resolved. At this time, the most prominent warlords in China were: Yuan Shao, who controlled Ji, Bing and Qing provinces (covering most of present-day Hebei, Shanxi and Shandong). Some of the territories were governed by Yuan Shao's three sons (Yuan Tan, Yuan Xi and Yuan Shang) and nephew (Gao Gan). Yuan Shu, who controlled most of present-day Anhui and parts of Jiangsu Gongsun Zan, who controlled You Province, including present-day Beijing, Tianjin and western Liaoning Liu Biao, who controlled Jing Province (covering present-day Hubei and Hunan) Liu Zhang, who controlled Yi Province (covering the Sichuan Basin) Lü Bu, who seized control of Xu Province (covering present-day northern Jiangsu) from its previous governor Liu Bei There were still many other minor warlords, and Cao Cao particularly sought to get them to submit to him. In 197, Zhang Xiu surrendered Wancheng to Cao Cao. However, Cao Cao later had an affair with Zhang Xiu's widowed aunt, angering Zhang. Zhang, who learned of Cao Cao's planned assassination on his life, rebelled and launched a surprise attack on Cao Cao at Wancheng. In this battle, Cao Cao's eldest son Cao Ang, nephew Cao Anmin, and bodyguard Dian