sentences:  In the first month of 1234, the Mongols allied with the Southern Song dynasty and besieged Caizhou.Emperor Aizong sensed that his doom was near, but did not want to be remembered in history as the last emperor of the Jin dynasty, so he announced his decision to abdicate and pass his throne to Wanyan Chenglin.Wanyan Chenglin refused to accept, but the emperor insisted and said, "I am fat and unable to ride on horseback into battle.