In the Three Kingdoms, when did Shu decline? Guan Yu has a big responsibility because Zhang Fei died, which caused internal discord in Shu and led to the defeat of Yiling.

First, the fault lies with Guan Yunchang. General Guan should not have underestimated the enemy and Lu Meng, thinking that Lu Meng was still young, so he died in Maicheng. After Guan Yu's death, the morale of the Shu army was greatly reduced. Liu Bei and Zhang Fei wanted to retaliate. Qiu, refused to listen to Zhuge Liang's words and insisted on attacking Wu. Zhang Fei was so angry that he asked the soldiers to prepare white robes for combat within three days. The soldiers were afraid that they would kill Zhang Fei and put him in his tent because of the military order. As a result, the Kingdom of Shu lost two generals in just a few months, and the Kingdom of Shu gradually went to the bottom. If Guan Yu did not underestimate the enemy at that time, how could Liu Bei avenge Zhang Fei's death, so he passed Guan Yu

Second , the mistake was with Liu Bei. After the death of Guan Yu and Zhang Fei, Liu Bei was determined to avenge the state of Wu. He did not listen to Zhuge Liang's good advice and was determined to attack the state of Wu. Zhuge Liang had no choice but to allow it. Liu Bei thought he was well versed in the art of war, abused military skills, and underestimated the enemy. Suspicious, they rushed to attack and were trapped near Beichuan. The Wu army did not fight for a long time. Liu Xuande's army had difficulty in getting water. He refused to listen to dissuasion and insisted on encamping the army 700 miles away from the backing Yanshui. As a result, the 750,000-strong Shu army was completely destroyed. The army was destroyed. Yiyi died with Baidi City, Tuogu and Zhuge Liang, Yongzi-Liu Chan passed away as his queen. How could he have ended up like this if Liu Bei hadn't not listened to Zhuge's good advice, which made the Shu army further decline after the death of Zhang Fei and Guan Yu

Third, it was Zhuge Kongming’s fault. At that time, the Shu army was called to attack the Wei State. They won successive victories in the first battle. Then they encountered Sima Yi’s comeback. Then he sent Ma Di to guard the street pavilion. Ma Di only talked about military affairs on paper and did not know how to use troops. He agreed with the street pavilion. After the defeat of Wei, Zhuge Kongming knew that Ma Di was incompetent and asked Ma Di to guard the street pavilion, which was a dereliction of duty. If Zhuge Liang succeeded in conquering Wei, maybe Shu could move to the top step by step from then on, but because of Jieting After the fall, Zhuge Liang had no choice but to do it

Fourth, the fault lies with Liu Chan. Everyone knows that Liu Chan is mediocre and incompetent. He only thinks that with Zhuge as his father, everything will be fine. He ignores the government and is playful all his life. He is really a fool. It is difficult for Zhuge Liang alone to make a comeback. The mediocre government has led to perennial rebellions in the south, and Liu Chan cannot escape his responsibility.