On the surface, the reason is simple, that is, Chu Huaiwang once said, "The one who enters the customs first is king". According to this statement, Liu Bang should be the king of Qin, and he already means Wang Guanzhong. He has sent someone to guard Hangu Pass. Unfortunately, Xiang Yu's army has arrived. Liu Bang had to submit to humiliation and went to Hong Men to confess to Xiang Yu, saying that he would never dare to be the king of Qin, just guarding the place for Wang Xiang. Later, Xiang Yu entered the customs, burned Xianyang Palace, returned to Pengcheng, and sealed the vassal. In order to avoid public opinion, he was embarrassed not to give Liu a piece of land, so he gave him the land of Shu. In other words, Liu Bang was originally the King of Shu. Later, in order to seek an open hand, Liu Bang bribed Xiang Bo to add another piece of Hanzhong to become the real Hanwang. At this time, the land of Qin has been divided among Zhang Han, Wang Ming and Sima Xin.