What was the role of grain and grass in ancient wars?

Without food and grass, the morale of the army will be scattered. Many soldiers don't want to fight because the war is very fierce. Many soldiers fight for their lives. Show the landlord the battle of Changping. In 262 BC, Zhao Haoqi, the state of Qin, sent a general to attack South Korea, occupied the wild king city, and cut off the contact between Shangdang County and the capital of South Korea. South Korea wanted to sacrifice Shangdang County to make peace with Qin, but the defenders of Shangdang County refused to surrender to Qin, so Zhao sent troops to take Shangdang County. In the forty-seventh year of Zhao Haoqi (260 BC), the Qin Dynasty sent Wang Shu, the eldest son of Zuo Shu, to attack North Korea and seize Shangdang. Shangdang fled to Zhao, and Zhao was stationed in Changping to appease Shangdang. In April, the King of Yue attacked Zhao. Zhao sent Lian Po to resist. Zhao foot soldiers ordered Qin to denounce the soldiers, and Qin denounced the soldiers to chop Zhao Bijiang eggplant. In June, he defeated Zhao and captured two armies and four armies. In July, Zhao Jun built a wall to defend. Qin Jun attacked the Zhao wall again, took the second commandant, and broke the array to seize the Western Wall. The two sides were deadlocked for many days, and Zhao Jun suffered huge losses. According to the situation that the enemy was strong and we were weak and lost in the first battle, Lian Po decided to stick to the camp and prepare to attack Chi. Many times, Zhao did not send troops. The prince of Zhao repeatedly blamed Lian Po for this. In response to Hou, the Qin Dynasty sent people to take their daughters to pay bribes to Zhao. They used deviant methods to spread rumors and said: "What Qin hates and fears is Zhao Kuo, the son of Ma Fujun Zhao She; Lian Po is easy to deal with, and he is about to surrender. " The prince of Zhao resented Lian Po's defeat, suffered heavy casualties and earned Lian Po's stubborn refusal to fight. So he listened to rumors, sent Zhao Kuo instead of Lian Po as the general, and ordered him to lead troops to attack the State of Qin. After Zhao Kuo came to power, the deployment of rebelling against Lian Po not only changed the military system in the war, but also replaced a large number of generals, which made Zhao's combat power decline. When Qin saw Zhao Zhongji, he secretly ordered Bai Qi to be the general and Wang Bi to be the lieutenant. Zhao Kuo is arrogant, but he is afraid to start from scratch. The king of Qin ordered that "whoever dares to vent his anger on Wu Anjun will be beheaded." In the face of reckless and arrogant opponents, Tian Lei decided to retreat to lure the enemy, divide and panic. He ordered the border guards to take on the task of luring the enemy. When Zhao's army attacked, he pretended to be defeated and retreated. He deployed the main force in depth to build a bag-shaped position, and sent another 5 thousand troops to wedge between the enemy vanguard and the main force, waiting for an opportunity to split the Zhao army. In August, Zhao Kuo rashly took offensive action without knowing the actual situation. Pretend to fail, and secretly spread his wings to build Indiana Jones to intimidate Zhao. By the time Zhao attacked the pass, Qin was ready, and the pass was strong and could not be entered. Tian Lei ordered Indiana Jones to attack quickly and cut the Zhao army into three sections. Zhao Jun separated from head to tail, and the route for providing foodstuff was broken. Send hussars to harass Zhao. Zhao's war situation was critical, so he had to build a wall to support reinforcements. When the King of Qin heard that the grain and grass supply of Zhao was cut off, he went to Hanoi to supervise the war, recruited Ding Congjun, a male over 15 years old, and awarded him the rank of civilian, so as to stop the reinforcements and grain of Zhao and fight against Zhao with all his strength. By September, Zhao Bing had been hungry for 46 days and even committed suicide. Desperate, Zhao Kuo regrouped his troops and divided them into four teams, which broke through in turn, but never got out. Zhao Kuo led a good soldier and was shot by Qin Jun. Zhao Kuo's army was defeated. 400,000 soldiers surrendered in vain. In vain, he tricked and killed all Zhao's soldiers, leaving only 240 soldiers to report back to Zhao. Zhao was stunned by it.