In the southeast of Cao Wei, the influence of Sun Quan in Jiangdong lies. In 228, Lu Xun had just defeated Cao Xiubu of Cao Wei in Shi Ting War, which was a great threat to Hefei in the southeast of Cao Wei, Huainan and Jingzhou in the south.
To the west of Cao Wei is the rising Xianbei Xiongzhu Ke Bineng. On the one hand, Kirby can surrender to Cao Wei, on the other hand, he can launch a tribal unification war. Without the interference of Cao Wei, Kirby could unify the ministries of Xianbei without much problem. It was because of Cao Wei's interference that Kirby began to openly rebel against Cao Wei, and once joined hands with other Xianbei Khan, such as Budugen.
When Cao Cao was preparing to take part in the Hanzhong War, there was a rebellion on the northwest border, which was caused by Ke Bineng. Cao Cao sent Cao Zhang to pacify, and Zhuge Liang joined forces with Kirby to send troops to contain Cao Wei in the fourth Northern Expedition. The existence of Kirby in the northwest posed a considerable threat to Cao Wei.
To the north of Cao Wei is Liaodong Gongsun Yuan. In 228, Gongsun Yuan just seized the position of his uncle Gongsun Gong, and once flirted with Sun Quan. For Cao Wei, he was rebellious and completely independent, and Cao Wei also defended Gongsun Yuan to the death.
To the southwest of Cao Wei is Shu Han led by Zhuge Liang. Zhuge Liang made five northern expeditions, one defeat, two wins and two draws. On the surface, Cao Wei's strength is several times that of Shu Han, its population is four times that of Shu Han, its territory is eight times that of Shu Han, and its talent, army and economic strength are several times that of Shu Han. Why not destroy Shu Han in one fell swoop?
In fact, Cao Wei did think so, and implemented it, but failed. That is Cao Zhen's massive felling of Shu in 230. As a result, because of the difficult road and bad weather, he went back halfway on the meridian valley road and returned in vain.
Yes, the road is difficult. Zhuge Liang's Northern Expedition is also a difficult road, and logistics supply is difficult. Fighting is a huge project. If there are100000 people fighting in front, at least 200000 people in the rear are in service, transporting food and grass, and being given personnel and materials. Difficulties in roads and transportation seriously affected the war.
This is only one of the reasons why Cao Wei failed to destroy Shu Han in World War I, not the main reason. Mainly the external environment of Cao Wei is not very good, and all four directions are enemies. If we concentrate on one direction, it will inevitably weaken the strength in other directions and give other enemies an opportunity.
In the era of cold weapons, national strength is important, but it is not the only factor that determines the victory of the war. There are many examples of national destruction caused by the failure of a war, such as the battle of Guandu, such as the battle of Feishui. Yuan Shao and Fu Jian were defeated, and the country was ruined. Similarly, Cao Wei did not dare to treat Zhuge Liang's Northern Expedition lightly.
In the face of enemies from all directions, Cao Wei not only placed heavy guards in the border areas, but also had a Central Army of about 50,000 to 80,000 people on standby. During Zhuge Liang's first Northern Expedition, Cao Wei not only sent most of the Central Army, but also the emperor Cao Rui himself. After eliminating Zhuge Liang's first threat, he still did not take it lightly, strengthened border defense and increased border troops.
Although Cao Wei's national strength is strong, he dare not put all his strength into dealing with Shu Han, because the war of national subjugation is a considerable battle, and unless Cao Wei excludes other potential threats, he dare not target Shu Han. The only way for Cao Wei is to change space, recuperate, restore national strength and solve other threats, so as to concentrate on dealing with Shu Han.
Otherwise, if Cao Wei falls into the quagmire of war and cannot win Shu Han, the enemies in other directions will be very dangerous. If not, Shu Han will not be destroyed, but it is possible that Cao Wei himself will be destroyed. Therefore, it is unrealistic to destroy Shu Han by World War I.
Moreover, at that time, there were many talents in Shu and Han, such as Zhuge Liang, and there was no basis for extinction. Although Cao Wei's national strength is strong, it is not enough to destroy a country at once.
In fact, when Zhuge Liang died in the Northern Expedition in 234, Sima Yi begged the emperor Cao Rui to lead an army south to destroy Shu Han, but Cao Rui disagreed. I think Cao Rui's decision was correct. Sima Yi was too early to destroy Shu.
In 234, Zhuge Liang died of illness, in 235, Bi Ke was assassinated, in 238, Gongsun Yuan in Liaodong was pacified by Sima Yi, and Cao Wei relieved the threats from the north, northwest and southwest in turn, which had the conditions and foundation to destroy Shu Han. But at this time, Cao Wei had fallen into infighting, at the same time, Cao Rui died, and the new emperor was young and would not go abroad to fight on a large scale.