In 221 AD, Liu Bei proclaimed himself emperor in Chengdu. After the establishment of the Shu Han Dynasty, they continued to send troops to the Northern Expedition. It can be seen that Liu Bei did not lack food and grass for more than a year when he was in power, and he did not worry about it. But after Liu Bei's death, Zhuge Liang had an important reason for failure in every Northern Expedition, which was the lack of food and grass. Three of the five Northern Expeditions had to return because of lack of food and grass.
According to the Records of the Three Kingdoms, during each Northern Expedition. Wei Yan wanted to separate his troops from Zhuge Liang and advance. Although Wei Yan wanted to launch a surprise attack in order to achieve victory, Zhuge Liang never agreed. Because the Shu Han was originally a small place, and the Northern Expedition was fought far away from home, transportation of food and grass was very difficult. There is no way Shu Han can compare with Wei in this regard. Fighting a war of attrition is simply asking for death. In this case, Shu Han must be trapped in food.
The transportation conditions in ancient times were very poor, and the Shu Han was based in the Bashu region. There is a poem that says that the road to Shu is difficult and it is difficult to reach the sky. Liu Bang was able to send troops from the land of Shu Han to compete with Xiang Yu, but he was still at a disadvantage. However, he did not seek stability. Instead, he secretly built a plank road to attack Chencang, raided three places, captured the Guanzhong area, and ensured the supply of food and grass.
In addition to achieving greater results during Zhuge Liang's first Northern Expedition, he sought stability every time and fell into the enemy's war of attrition again and again. Shu is a small country, and it fights far away from its homeland. A war of attrition means consuming food. Even if Zhuge Liang invented wooden oxen and flowing horses to speed up the transportation of food, he could not keep up with the speed at which the soldiers consumed food and grass.
In short, Liu Bang was able to send troops from Sichuan, and Chu and Han fought for 4 years, and never worried about food and grass. Zhuge Liang was repeatedly hampered by the problem of food and grass, mainly because Zhuge Liang was cautious and did not dare to take risks, so he started a war of attrition while seeking stability.