and yielded Yi Province to Liu Bei. The province became Liu Bei's new base, and he used the mountainous surroundings as natural defences against Cao Cao in the north. In the same year Liu Bei took over Yi Province, diplomatic relations between him and Sun Quan deteriorated when he refused to return Jing Province, which he "borrowed" from Sun Quan five years ago. Sun Quan launched an initial attack on Guan Yu and much of eastern Jing Province quickly submitted. However, after negotiations between Guan Yu and Lu Su, Liu Bei agreed to give up the three commanderies of Changsha, Jiangxia and Guiyang to Sun Quan, renewing their alliance and dividing Jing Province between them along the Xiang River. Yangping and Hanzhong Campaign (215–219) In 215, Cao Cao attacked Zhang Lu and defeated him at the Battle of Yangping. Zhang Lu surrendered and his domain in Hanzhong came under Cao Cao's control (January 216). Against the advice of his followers to move south and attack Liu Bei in Yi Province, Cao Cao withdrew his armies and left Xiahou Yuan in command of a small force to defend Hanzhong. The following year, Cao Cao pressured Emperor Xian into granting him a title of nobility, "King of Wei". Over the next few years, Cao Cao's style of living became more like the emperor's, and he also received greater honours. In 217, Liu Bei started a campaign to seize Hanzhong from Cao Cao. After Xiahou Yuan was defeated and killed at the Battle of Mount Dingjun in 219, Cao Cao became alarmed and quickly arrived with reinforcements to resist Liu Bei. Both sides became locked in a stalemate, except for a clash at the Battle of Han River, before Cao Cao eventually decided to withdraw his forces, giving up Hanzhong to Liu Bei. Liu Bei subsequently declared himself "King of Hanzhong" after his victory. Breaking of the Sun–Liu alliance (219–220) Around the time when Liu Bei was attacking Hanzhong, Guan Yu also advanced north from Jing Province to attack Cao Cao's city of Fancheng (樊城; present-day Fancheng District, Xiangyang, Hubei), which was defended by Cao Ren. While Cao Ren managed to hold on to his position firmly, Guan Yu besieged the city, and the situation was serious enough that Cao Cao even considered moving the capital away from Xu. At the same time, Sun Quan became increasingly resentful of Guan Yu because the