According to the information recorded in the History of the Three Kingdoms, Wei Yan's plan presupposes that it will take more than 20 days for Wei Jun's main forces to gather in Chang 'an after learning the news of the invasion of the Meridian Valley. By this time, Zhuge Liang's army had already left Gu Jie. But in fact, in real history, Cao Wei's main force not only rallied, but also advanced to Jieting and Qishan, hundreds of miles west of Chang 'an, defeated Zhuge Liang and retreated all the way, and then Wei Jun moved troops. It only took 50 days. Calculated, the time from Wei Jun to Chang 'an should not exceed 10 days. Wei Yan's assessment of the speed of Wei Jun's invasion was completely wrong, and he was probably caught off guard.
In addition, some people say that even if Wei Yan fails, he will only lose thousands of people, not more than the loss of street kiosks. This is not right. Wei Yan doesn't want to fight Yongzhou alone. He personally attacked Chang 'an and asked Zhuge Liang's main force to follow up from Gu Jie. So, according to his plan, the main force finally assembled in Chang 'an. Considering the aforementioned risk of beating Chang 'an, and the fact that the main force of Wei Jun might arrive twice as fast as he estimated, the result was that the main force of the Shu army fought a more unfavorable battle than in history under Chang 'an, and the losses were even heavier. As for this loss, it is hard to say whether Wei will go south on a large scale. After all, long-term development is better than Wei. But what is certain is that Shu Han will face more difficult days than in history.
According to Wei Yan, Wei Yan led five thousand soldiers to Chang 'an. Chang 'an is a magnificent city. The city is strong and easy to defend but difficult to attack. Only 5000 soldiers can occupy it? Besides, Wei Yan is a tired teacher. Let's just say it's hard. According to Wei Yan, Xia Houmao, the main force guarding the city, will directly abandon the city and flee. This is very unreliable. A large Chang 'an can't keep the attack of 5,000 soldiers. This is for defense, not to let you out of the city pk. Moreover, even if Xia Houmao escapes, all the generals in Chang 'an will follow. What if someone doesn't run away? Where is Wei Yan? Storm? That's death.
Besides, the famous Guo Huai is nearby. Wei belongs to the plain, and the support time only takes one or two days to arrive. Can Wei Yan win in such a short time? If Wei Yan takes Chang 'an, can his 5,000 soldiers stop Wei Jun's attack? Waiting for Zhuge Liang's support? Zhuge Liang arrived in Chang 'an. According to the expert's budget, it will take twenty days at the earliest. Can Wei Yan's 5,000 soldiers last this long? Waiting for Zhuge Liang to come to help? If it takes three days for Wei to support Chang 'an, then Wei Yan has to let go of the Wei Jun 17-day attack so that Zhuge Liang can arrive and Wei Yan can hold on?
If Wei Yan succeeds in waiting for Zhuge Liang's support and Zhuge Liang enters Chang 'an, then the next result is that the Shu army will face Wei Jun head-on. Can the Shu army beat Wei Jun? Tens of thousands of troops of the Shu army fought against their opponents, and the battle of Chang 'an Plain, Wei Jun fighters, and the Shu army fought against them. Shu army is suitable for field operations, while Wei Jun is suitable for plain operations. How to fight the Shu army in Chang 'an? If Wei Jun does not attack by encircling and cutting off the enemy's route for providing foodstuff, the Shu army will be defeated without a fight. Once the Shu army enters Chang 'an, Chang 'an will become an isolated city of Shu. Without support, confrontation with Wei is to die, and the final result is to rush out of Cao Wei in Wei Jun and return to Hanzhong, so a city like Chang 'an is meaningless.
If Wei Yan was attacked by Wei Jun when he was waiting for Zhuge Liang in Chang 'an, and the news was blocked, and then he ambushed Zhuge Liang to lead the army and then completely annihilated it, wouldn't Shu be destroyed in advance? Or Wei Jun ambush in this place in advance, Wei Yan is not completely annihilated? But with Xia Houmao's talent, there should be no IQ, but Xia Houmao will not be powerless and afraid of Wei Yan's five thousand soldiers. But when Cao Zhen and others arrived, Wei Yan was not so lucky.
Although the meridian valley was a clever idea, it was not applicable in the circumstances at that time. It is meaningless to take Chang 'an alone. There is no other dangerous place as a barrier. Chang 'an is an isolated city for Shu Han. In the process of taking Chang 'an, there are too many influencing factors and too many risks. The most important commander in chief of Wei is Cao Zhen, not a brave man. Cao Zhen's military talents can be played with Zhuge Liang for a while, but absolutely not.