In 234 AD, Zhuge Liang led the Shu Han army to carry out the Fifth Northern Expedition, when Zhuge Liang's troops fought with Sima Yi for more than a hundred days in Wuzhangyuan, but because Sima Yi was afraid of Shu Han's troops, he was afraid and did not fight Zhuge Liang, resulting in Zhuge Liang being successfully dragged to death by Sima Yi. Before Zhuge Liang's death, he arranged the aftermath in advance in order to avoid the shu Han army being harmed during the retreat, when Zhuge Liang asked Wei yan to cut off, Jiang Wei followed, and handed over the position of commander to Yang Yi. However, Wei Yan was dissatisfied with Zhuge Liang's explanation, and he sent an army privately to cut off the Retreat route of the Shu army, and was eventually killed by Ma Dai sent by Yang Yi. That is to say, during the Fifth Northern Expedition, Shu Han not only lost zhuge Liang, but also lost the general Wei Yan, but Wei Yan had the intention of plotting rebellion, so for Shu Han, the loss was not great?
In fact, Wei Yan's death was a very great loss for Shu Han. It should be known that after Wei Yan's death, the Fifth Northern Expedition was a complete collapse. After all, both the Romance of the Three Kingdoms and the Wei Luo record that Wei Yan intended to continue the Northern Expedition after Zhuge Liang's death, and in the Wei Luo, it is even recorded that Zhuge Liang initially handed over military power to Wei Yan, but Wei Yan was later killed by Yang Yi for personal reasons, and no one among the senior generals proposed to continue the Northern Expedition.
In fact, the Northern Expedition at that time did not have any strategic and tactical problems, the two armies faced each other, Shu Han was never defeated, Tuntian was also very smooth, there was no problem in the rear, and there was no record that Zhuge Liang was not in the army's turmoil, so the Northern Expedition at that time could indeed continue, perhaps, the Northern Expedition at that time may still be victorious, but at that time, Jiang Wei and others advocated retreating and lost the last chance of Shu Han. It can be said that after Zhuge Liang's death, it was not the end of the Fifth Northern Expedition, and Wei Yan was killed before it could be called.
Moreover, after Jiang Wei led Hanzhong, he changed the policy of using terrain defense in Hanzhong established during the Wei Yan period to become a more aggressive policy of luring the enemy to go deep and intending to defend and counterattack, and the direct result of this was that during the Battle of Wei and Shu, Jiang Wei and Zhong Hui fought at The Sword Pavilion, rather than the two sides holding each other in Hanzhong, providing the possibility of Deng Aiyinping's smuggling, and this directly led to the fall of Shu Han. If Wei Yan is still there, it should be that the two sides fought a great war in Hanzhong, and Shu Han relied on natural dangers to defend to the death, who knows that the country will not perish. What's more, during the Jiang Wei period, there had been such a thing as the gaopingling change, and Wei Yan was likely to seize the opportunity to go north again and make breakthrough progress in this regard, so the result was naturally much better than Jiang Wei's northern expedition.
The author believes that wei Yan's death directly affected the later development of Shu Han, so Wei Yan's death in the Fifth Northern Expedition was a great loss for Shu Han.