In 215, Cao Cao attacked the warlord Zhang Lu in Hanzhong , defeating the latter at the Battle of Yangping. Zhang Lu surrendered and Hanzhong came under Cao Cao's control. On Liu Bei's side, he had also recently seized control of Yi Province (covering present-day Sichuan and Chongqing) from Liu Zhang, and was in the midst of a dispute with his ally Sun Quan over Jing Province (covering present-day Hubei and Hunan). Liu Bei felt threatened when he received news that Hanzhong had fallen to Cao Cao, because Hanzhong was the northern "gateway" into Yi Province, and he was now in danger of losing his home base to Cao Cao. Hence, Liu Bei came to a border treaty with Sun Quan, who had seized Changsha (長沙), Guiyang (桂陽), and Lingling (零陵) from him. Liu Bei asked Sun Quan to divert Cao Cao's attent