The battle line is too long:
In fact, the walnut area has always been called a battleground for military strategists. There is plenty of groundwater in your Hetao area, and there are large areas in the walnut area. Oasis can play a key role in economic development and military presence. However, the walnut area has long been occupied by ethnic minorities, such as the Tangut in the Han Dynasty, such as the Xiongnu in the late Eastern Han Dynasty, so it is very difficult to occupy the Hetao area. At that time, because the Shu-Han front was too long, it was impossible to divide our forces to deal with the Hetao area!
Ethnic minority blocks:
Ethnic minorities ruled a large area of Hetao during the Cao Wei period and defeated Cao Wei many times. For example, the Xiongnu, the Tangut and the unknown ethnic group called Sanqi ... If you want to conquer the walnut area, you must defeat these ethnic minorities. At that time, Cao Jun's strength was not enough to spread all over China, because it was difficult for him to separate a large number of troops from the Shu-Han War. At the same time, it is also very difficult to crack down on ethnic minorities from the stationed border guards! The tenacious resistance of ethnic minorities has also become one of the important reasons why Cao Wei failed to occupy the Hetao area!
Insufficient military reserves:
In fact, Cao Wei's military strength in that year was already a spent force, because after the war with Wu and Cao Wei, the combat effectiveness was greatly injured and Cao Cao's army suffered serious losses, so Cao Wei did not have enough ability to occupy other areas. Moreover, there was a serious shortage of military reserve forces at that time, but the reserve forces were mainly manifested in the shortage of military supplies and food supply, which was as important as the reserve supply in previous wars!