First, the national strength of Shu began to decline. Look at Zhuge Liang's early Northern Expedition. He led 300,000 troops and Jiang Wei almost 200,000. (The decline in available troops is a manifestation of the decline in weapons productivity and grain production. This shows that Shu's national strength is weak.

Second, Jiang Wei himself is not as good as Zhuge Liang. No matter in tactics, tactics and strategies, Jiang Wei's prestige in the Shu army is not as good as that of Zhuge Liang. This can be learned from Si Mazhao's later words: "Liu Chan, the master of Shu, is weak and incompetent, and can't be supported for a long time, let alone Jiang Wei?" Jiang Wei himself said that he was not as good as Zhuge Liang.

Third, there is a shortage of talents in Shu, and civil servants and military commanders have died one after another. Shu is blocked in the Sichuan Basin and cannot be compared with the exchange of talents in the Central Plains. In the later period, the imperial palace lacked the supervision of good ministers. In the original model, Zhuge Liang mentioned that "Fei Yi, Dong Yun, Jiang Wan and Guo Yizhi" and others were all dead, and there was no heir, which led to eunuch tyranny. Externally, it turned out that Liu Bei and Liu Zhang's aides were all dead, and there were no good generals available, so that in the end, Jiang Wei was alone in Jiange, Wargo sneaked into level tone, and there was no decent military commander in Chengdu.

Fourth, Liu Chan, the late ruler, was so incompetent that he listened to the eunuch's words and indulged in debauchery that all court ministers had a "concession heart", listened to Huang Hao's slanders and alienated the relationship with Jiang Wei and others. (When Jiang Wei gained an advantage in the Northern Expedition, he listened to Huang Hao's slanders and recalled Jiang Wei and his army. ) Jiang Wei had to listen to the doctor's slanderers. The overall defensive strength of Shu has declined sharply.

Fifth, Wargo and others were resourceful and saw through Jiang Wei's strategy many times and held Qishan. There are many talented people in Wei, including Zhong Hui, Jia Chong, Zhang Qian and Zhuge Xu.

Sixth, many years after the demise of the Han Dynasty, the nostalgia of the Central Plains people for the Han Dynasty has gone to zero. Even later, Chang 'an people did not say Shu Han to Xishu people, but only said the word "Shu people". The rule of Cao Shi's regime in the Central Plains was relatively successful, and the nostalgia and yearning of the people in the Central Plains for the Han Dynasty was almost gone. This is also a question of "popular support". Liu Chan's later performance in West Shu was another "bad king" who favored eunuchs, just like the "ten constant attendants" when he visited the Emperor and the Spirit Emperor at the end of the Eastern Han Dynasty, just like history repeating itself. God wants Shu Han (Han Dynasty) to perish, and no one can save it.

As for the benefits of the Northern Expedition:

You can refer to Zhuge Liang's Model for Later Generations. Generally speaking, the Northern Expedition is "defending by attacking", which is a good thing. Because if the Northern Expedition is not carried out quickly, the officials of Sichuan and Sichuan dynasties under Liu Bei and Liu Zhang will die one after another, and the civil servants, military commanders and soldiers who have been tempered by various wars will also die one after another. Moreover, Liu Bei recruited a large number of able-bodied men in the previous Wu War. When the Wu War failed, Sichuan and Shu lost their vitality. If we can't turn passivity into initiative and expand talents, Shu will be "waiting for death", as can be seen from Zhuge Liang's example. Therefore, the Northern Expedition is passive, but it is a "strategy" of "gambling" with talents and experience accumulated over the years. It should be said that it is a good thing. War consumes national strength, which is inevitable. War itself is a "gamble" between two countries, and there must be a price.