Zhuge Liang's Northern Expedition occupies an important place in the history of the Three Kingdoms, and the motives and strategic considerations behind it are far-reaching and complex. Judging from the three main aspects you provided, Zhuge Liang's Northern Expedition was not only a military operation, but also a comprehensive consideration of politics, economy, strategy and even psychology.
1. In order to repay the emperor, in order to fulfill his last wish
Zhuge Liang's words in "The Teacher's Table" profoundly expressed his gratitude to Liu Bei for his kindness, as well as his sense of responsibility for reviving the Han family and honoring the ancestors. This deep friendship and sense of moral responsibility became an important driving force for his Northern Expedition. Zhuge Liang hoped that through the Northern Expedition, Liu Bei's unfinished business would be realized, and at the same time, he would also prove his loyalty and ability.
2. If Cao Wei is not attacked, Shu Han will die
From a strategic point of view, Zhuge Liang realized that if Cao Wei was given time to develop national power, the gap between Shu and Wei would further widen, which could eventually lead to the demise of Shu Han. Therefore, he chose to take the initiative and weaken Cao Wei's strength through the Northern Expedition, while fighting for more living space for himself. The occupation of Yongzhou and Liangzhou can not only obtain strategic resources, such as Qinchuan horses, but also provide Shu Han with greater strategic depth and detour space, and enhance its flexibility and initiative in combat.
3. The Northern Expedition to the Central Plains diverted contradictions
Within Shu Han, the contradictions between the Jingzhou Group, the Dongzhou Group and the Shudi Group became increasingly acute. Through the Northern Expedition, Zhuge Liang successfully transferred these internal contradictions to the external contradictions against Cao Wei. This strategy not only eased tensions within Shu Han, but also strengthened the cohesion and centripetal force of the state. At the same time, the success of the Northern Expedition will also bring greater political and military benefits to Shu Han, help to enhance the status and influence of the Jingzhou group, and further consolidate its ruling position.
Zhuge Liang's Northern Expedition was a wise choice he made in a complex political, economic, and strategic environment. Through the Northern Expedition, he not only realized his personal and national ideals, but also successfully alleviated internal contradictions, and won more time and space for the survival and development of Shu Han. Although the Northern Expedition ultimately failed to fully achieve the goal of recovering the Han Dynasty, Zhuge Liang's wisdom and courage were forever engraved in the long river of history.