Zhuge Liang thinks that this plan is pending, and the main question is whether Wei Yan can win Chang 'an in a short time, otherwise he may be surrounded by Guo Huai, the secretariat of Yongzhou, who is closely related to him, and Kanto reinforcements from Ma Pingchuan at any time in the confrontation. Secondly, whether Wei Yan can hold on to Zhuge Liang's reinforcements after winning Chang 'an depends on the situation of Guo Huai and Kanto reinforcements.
1. Wei Yan started from Bao, along the east of Qinling, entered the Meridian Valley, and followed the Meridian Valley to Chang 'an. This March must be completed within 10 days. Zhuge Liang's army must arrive in Chang 'an (or Tongguan) from Gu Jie to meet Wei Yan within 20-30 days.
The meridian passage, with a total length of more than 300 kilometers, is confronted by mountains on both sides, and the water in the middle is swift. In this road condition, it is difficult for cars to move at full speed, let alone people leave, and the whole meridian passage depends on the plank road on Xiuyan. If there are many shortcomings, it will take a lot of time to repair them, which will seriously affect the marching speed. In this case, can Wei Yan guarantee to cross the Meridian Valley to reach the gate of Chang 'an City within 10 days? In the same way, Zhuge Liang's army set out from the inclined valley and took the plank road, facing the same problems as Wei Yan. Can it reach Chang 'an in 30 days? Obviously, it is also an unknown number.
In fact, two years later, when Cao Zhen was on the Western Expedition, the army horse walked in the Meridian Valley for a month, and its difficulties can be imagined.
2. It is said that Xiahou Mao, the commander-in-chief of Cao Wei's Chang 'an, heard of the arrival of soldiers and abandoned the city and fled.
Xiahou Mao is a playboy, a dude. I don't know the art of war, strategy, war, courage and plan. Wei Yan thinks that Xiahou Mao thinks that Zhuge Liang will send troops according to the routine and will inevitably send all his troops to the front to stop Zhuge Liang's army. Chang 'an can't have too many troops. Even though he has more troops than Wei Yan, he has never fought a war, and his ability to adapt to cold weather is poor and his intellectual function is low. He didn't know how many people there were in Wei Yan. He must have abandoned the city in fright.
But what if he sticks to the city instead of running away? Wei Yan marched in a hurry and could not bring enough siege equipment. Chang 'an is high and deep, easy to defend but difficult to attack. Yongzhou secretariat Guo Huai is close at hand. Xia Houmao insisted, and Guo Huai came to the rescue as quickly as possible. Aren't Wei Yan's troops wrapped up in jiaozi?
Third, Xiahou Mao had to leave a lot of food when he fled.
How much food can Wei Yan bring with him when he raided Chang 'an? Even with more, it is estimated that Chang 'an will be out of food at the gates, right? How can the grain be transported there, because the grain transportation routes are all Cao Wei's territory. Even if Xiahou Taizu really runs away, will he leave you enough food in the city? Will he destroy the food conveniently?
Fourth, the sneak attack kept zero information leakage, which made Wei Guanzhong and Nanyang completely deaf.
Because of Chang 'an's strategic position and guards at that time, Cao Wei set up many defense lines, so even if Wei Yan succeeded in a quick surprise attack, he must ensure that the news was completely confidential. Cao Wei, the soldiers and civilians in Guanzhong and Nanyang areas are unaware of it, so that they can successfully reach Chang 'an at the gate, otherwise they will be directly discovered by the local defenders, and that is the point of no return.
It will take 20 days for Cao Wei's Kanto reinforcements to arrive in Chang 'an.
Besides, Wei Jun is from Guandong to Guanzhong, with convenient transportation and Ma Pingchuan. Zhuge Liang's army will take the thousands of miles plank road in the inclined valley. How to ensure to arrive in Chang 'an before the Kanto reinforcements? One thousand left behind, Wei Jun just ate Wei Yan first, then blocked the news, and earlier and earlier, Zhuge Liang's main corps was fished out of Xiegu Road, so they got together. After that, the consequences were unimaginable. If so, Zhuge Liang's main army will be wiped out.
Therefore, in Zhuge Liang's view, surprise attack is doomed to failure, and it is better to be slow and steady than to die in vain.
From the political point of view of Shu Han at that time, Zhuge Liang completely controlled the sovereignty of Liu Chan in his own hands. Once Zhuge Liang captures Chang 'an, Shu Han will definitely move to Chang 'an. Zhuge Liang's series of actions will make the world think that Zhuge Liang of Shu Han will be the second Cao Cao, and the resulting public opinion pressure is enormous. It is impossible for Liu Chan not to know about it. Judging from a series of actions of Liu Chan after Zhuge Liang's death, he was disgusted with Zhuge Liang's thumbtacks. As a wise man, Zhuge Liang will surely foresee that after capturing Chang 'an, the whole Shu Han will be on the verge of bankruptcy because of himself. In order to continue the Shu Han Dynasty, Zhuge Liang had to make a strategic plan to go west to Longyou, hoping that he would continue the Northern Expedition and the Northern Expedition would be defeated repeatedly. His bottom line is that he can't capture Chang 'an, because Zhuge Liang is very clear about the consequences of capturing Chang 'an and what will happen to the court of Shu and Han.
Zhuge Liang's ultimate goal is the Northern Expedition, which seems to be very sure and is a safe and secure plan. However, the battlefield situation is changing rapidly. From the historical reality, Zhuge Liang's so-called best laid plans never had the hope of complete success in the five northern expeditions from 228 to 234. The objective result is to contain, harass and weaken Wei. As long as he exists, Wei Liangzhou and Yongzhou dare not disarm, and Wei is always nervous about his expedition and dare not add soldiers. This may be his real strategy. The Northern Expedition will naturally succeed. If not, at least give Wei a headache and he can go back safely. As he himself said in Longzhong Dui, the premise of the success of the Northern Expedition is that the Central Plains has changed, so Zhuge Liang's attacks are mostly offensive and defensive.