One: equal with Cao Pi and raise the banner of the Han Dynasty.
Liu Bei started with the slogan of "Reviving the Han Dynasty", and so did the final grand strategy formulated in Longzhong Dui. After Cao Pi usurped the Han Dynasty, Liu Bei's strategic slogan disappeared. No matter whether Xian Di is still here or not, the legal reasons do not exist. Therefore, a flag must be raised again immediately.
According to the Records of the Three Kingdoms, both the imperial edict of the minister who induced Liu Bei to become emperor and the imperial edict made public to the world after he ascended the throne stated that Cao Pi usurped the throne, destroyed the Han Dynasty and stole artifacts. Liu Bei Group can't recognize the legitimacy of Cao Pi's throne, but it also has to fight against Cao Pi in name.
Moreover, from Liu Bei's personal feeling, it is intolerable for Cao Pi to be an emperor. He is just a king of Hanzhong. Liu Bei is different from Sun Quan. Sun Quan has always been lower than Cao Cao and Liu Bei in birthright, and he is also a contemporary with Cao Pi. Therefore, Sun Quan can temporarily accept the submission to Cao Pi. Liu Bei is Cao Pi's elder, but he can't bow to the younger generation.
Second: boost our morale.
When Cao Pi usurped the Han Dynasty, Jingzhou fell and Guan Yu was killed, which dealt a great blow to the morale of Liu Bei Group. It turns out that Liu Bei Group owns Jingzhou, Yizhou and Hanzhong, which is known as "Woye is a thousand miles away and a million soldiers", and its overall strength exceeds Wudong Sunquan Group. If you have enough time to integrate your own strength, the northern expedition to Cao Wei is not an invisible dream.
But after Guan Yu's defeat, Liu Bei Group was strategically locked in Yizhou. If there is no basis for Hanzhong to make progress, it is basically possible to announce Liu Bei Group's withdrawal from hegemony in advance. Everyone is hesitating, and Cao Pi succeeded in usurping the Han Dynasty. In order to boost his morale, Liu Bei must also be proclaimed emperor, and at the same time promote his own civil and military officials, so that everyone has hope.
Third, the points and basis for the eastward expedition to Wu Dong.
After Liu Bei proclaimed himself emperor, the first thing he did was to crusade against Wu Dong, nominally to avenge Guan Yu, but in fact he wanted to recapture Jingzhou and even completely destroy Wu Dong. You need a name to send troops. Only when you are proclaimed emperor and then attack Wu can you have your birthright and basis. Liu Bei's dynasty is a continuation of the Han Dynasty, so the territory of the world should be his birthright, and Sun Quan has changed from an equal vassal to a rebel, so you can send troops with confidence.
Moreover, the influence of Guan Yu's loss of Jingzhou on Liu Bei Group also needs to be recovered. As we all know, the real rise of Liu Bei Group is the absorption of Jingzhou family. Now that the hometown of his most powerful group is gone, Liu Bei must make a choice to help them regain their hometown. Otherwise, the Yizhou family, which was already dissatisfied with Liu Bei, would be coke. In their eyes, the Jingzhou family has become a group of lost dogs, with more confidence.
Therefore, in view of the above reasons, even if Liu Bei's strength is not as good as others, he should be the emperor, not worse than his main rival Cao Wei, and he needs a sense of justice and fame in his western expedition. Internally, we should also calm the panic of Jingzhou faction who followed him into Yizhou. Don't say that after being proclaimed emperor, you can at least give your subordinates a promotion immediately, give them hope and encourage yourself at the same time.