Zhuge Liang's intelligence was rare in a hundred years, and even the last Northern Expedition he experienced before his death contained his plan. During the Shu State's Fifth Crusade against the State of Wei, Zhuge Liang secretly contacted Sun Quan to form an alliance, and Sun Quan agreed to sneak attack the State of Wei. Sun Quan led an army of 100,000 to attack Cao Wei, but was defeated by the army led by Emperor Ming of Wei. At Wuzhangyuan, the Shu army repeatedly lured Sima Yi out of the city, but all ended in failure. Sima Yi wanted to drag down the Shu army by refusing to face the battle, so that the Shu army would retreat without a fight.
Zhuge Liang also expected Sima Yi's thoughts, of course, he was also aware of the strength of the enemy and us, and he couldn't help but get anxious. He finally fell ill during a tour, and he was very worried about the Shu army in Wuzhangyuan, they were the only military force in the Shu kingdom, and if they were surrounded and annihilated by Sima Yi, the Shu state would be in a precarious situation. In this case, the best way was of course to let Zhuge Liang personally command the retreat, but Zhuge Liang's health was not as good as before, and he expected that he would not be able to support the Shu army and return to Hanzhong safely.
Wei Yan
For the sake of the Shu Kingdom's Jiangshan Sheji, he came up with a poisonous plan in desperation, that is, to give up the car to protect the marshal. In the army at that time, Wei Yan's merits were the most outstanding, and his qualifications were the oldest, but he was the main warrior faction, and zhuge Liang was really uneasy about the matter of retiring the army. The civilian official who held the opposite attitude to him was Yang Yi, who had always obeyed Zhuge Liang's orders, but he was not sincere, and his personality was lonely and arrogant, afraid that after Zhuge Liang's death, no one would be able to control them. Therefore, Zhuge Liang thought of using the contradictions between the two of them to steadily retreat.
Yang Yi
Zhuge Liang secretly received Yang Yi and personally entrusted him with the matter of retiring the army. Wei Yan secretly resented that Zhuge Liang had not summoned him, so after Zhuge Liang's death, their contradictions intensified. Yang Yi slowly retreated according to Zhuge Liang's instructions, but Wei Yan rushed to Nangukou before Yang Yi, and Wei Yan ordered his generals to fight with Yang Yi's army, but his men were reluctant to obey his orders. So Wei Yan fled in a panic, and at this moment, Ma Dai, who had been waiting for a long time, rushed forward to behead Wei Yan. After Jiang Wei was ordered to cut off the large army, Sima Yi heard the news of Zhuge Liang's death and immediately sent troops to pursue and kill him, and Jiang Wei launched Zhuge Liang's wooden statue, and Sima Yi shouted that he was deceived and fled into the wilderness.
In this way, Yang Yi's army retreated to the Shu kingdom in peace and security, and Yang Yi should have been a major contributor to this operation, but Liu Chan still made Yang Yi a Chinese military division according to Zhuge Liang's last words before his death, and had no real power, but promoted Jiang Wan. In this regard, Yang Yi was indignant every day, and some gossip reached Liu Chan's ears, so he deposed Yang Yi as a commoner. This retreat operation seems simple, but if there is a wrong step, it will cause the result of losing everything, and Zhuge Liang's clever calculation has made the Shu kingdom last for 29 years.
bibliography:
Romance of the Three Kingdoms