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Congratulating Sun Quan on becoming emperor

Around May 229, Sun Quan, the ruler of Shu's ally state Wu, declared himself emperor and put himself on par with Liu Shan of Shu. When the news reached the Shu imperial court, many officials were outraged as they thought that Sun Quan had no right to be emperor, and so they urged the Shu government to break ties with Wu. Although Zhuge Liang agreed that Sun Quan lacked legitimacy, he considered that the Wu–Shu alliance was vital to Shu's survival and long-term interests because they needed Wu to help them keep Wei occupied in the east while they attacked Wei in the west. After concluding that Shu should maintain the Wu–Shu alliance and refrain from criticising Sun Quan, he sent Chen Zhen on a diplomatic mission to Wu to recognise Sun Quan's claim to the throne and congratulate him.