After murdering Ma Teng, Cao Cao wanted to take advantage of Zhou Yuxin's death to invade Soochow and destroy Sun Quan. Just then, a detective reported to Cao Cao that Liu Bei was training the army, building weapons and preparing to capture Xichuan. Cao Cao was shocked when he heard this. He knew that if Liu Bei occupied surprisingly, his wings would become increasingly full, and it would be even more difficult to attack Liu Bei at that time. Cao Cao wanted to attack Liu Bei, but he was afraid of losing the good opportunity to destroy Wu. Just as he was hesitating, Chen Qun, the counselor, offered a plan and said, "Now Liu Bei and Sun Quan are in an alliance of lips and teeth. If Liu Bei takes Xichuan, the Prime Minister can order people to lead troops straight to the south of the Yangtze River, and Sun Quan will definitely ask Liu Bei for help. And Liu Bei only thinks about giving up, and he must have no intention to rescue Sun Quan. "In this way, we will first capture Dongwu and pacify Jingzhou, and then we will slowly plan to go west." When Cao Cao heard this, he was enlightened and led an army of 3, people to attack Sun Quan of Soochow.

Faced with Cao Cao's aggressive momentum, Sun Quan panicked and immediately ordered Lu Su to send someone to Liu Bei in Jingzhou for emergency. When Liu Bei received Sun Quan's letter for help, he felt in a dilemma: if he only took Xichuan and ignored Soochow, it would definitely lead to the disintegration of the Sun-Liu alliance; Wouldn't it be a pity to support Sun Quan and give up surprisingly? While Liu Bei was undecided, Zhuge Liang, who had just returned to Jingzhou from Nanjun, offered a plan: "Your master doesn't have to send troops to Dongwu, and he doesn't have to stop attacking Xichuan. Just write a letter to persuade Ma Chao to attack Cao Cao, so that Cao Cao can't take care of both ends and let him withdraw his troops from Dongwu automatically." Hearing this, Liu Bei quickly sent someone with his handwritten letter to persuade Ma Chao to attack Cao Cao.

Ma Chao is the son of Ma Teng in Xiliang. Ma Teng was killed by Cao Cao. Ma Chao hates Cao Cao with gnashing teeth and always intends to kill Cao Cao and avenge his father. At the sight of Liu Bei's letter, Ma Chao led a 2,-strong army to the pass and captured Chang 'an and Tongguan continuously. Cao Cao hurried back to the northwest and had no intention of attacking Soochow.

a strategic situation map of princes competing for supremacy is actually a "network of relationships" in which forces from all sides contain each other. Zhuge Liang took advantage of the fact that all forces contained each other and presented Liu Bei with the strategy of "encircling Wei to save Zhao", which not only saved the precarious Dongwu, but also made Liu Bei take advantage of the gap to occupy Xichuan, laying the foundation for Shu to become one of the best in the future.