Battle of Fan Castle

The Battle of Fan Castle was fought between the forces of Shu lead by Guan Yu, and the forces of Wei and Wu under the command of Cao Ren and Lu Meng respectively. In an follow up to Liu Bei's seizing of Mt. Ding Jun, Guan Yu, who was stationed in Jing province at the time, decided to drive Wei out of Jing by laying siege to the Wei stronghold at Fan Castle. Cao Ren lead the defense admirably, but Guan Yu initially was very succesful by flooding the castle and capturing Pang De and Yu Jin. However, Lu Meng was making plans to seize Jing, and so while Guan Yu was in the north, he took his chance and swept across Jing. When Guan Yu learned that he had been cut off, he retreated to Mai Castle where he made his last stand, but was captured along with his son Guan Ping by Wu. When taken before Sun Quan, he was asked to serve but he refused and was executed along with Guan Ping.

Reason for Defeat
The defeat at Fan castle was due to mass betrayal both by Shu's long term ally Wu, and other Shu officers, such as Mi Fang and Fu Shiren who were to guard Guan Yu's rear immediately surrendered to the advancing Wu forces, and Liu Feng who refused to send reinforcements.

Aftermath
The incident infuriated Liu Bei, as well as his sworn brother Zhang Fei who took out his anger on his subordinates and was murdered. Despite the advice of his advisor and strategist Zhuge Liang and other generals, Liu Bei mobilized for war against Wu and despite having an incredible force that news of which caused Wu officials to turn pale, and several generous peace offerings by Sun Quan, he continued his advance but was forced to flee after the disastrous Battle of Yi Ling and died soon afterwards.