At the end of the Eastern Han Dynasty, Cao Cao's son Cao Pi took the lead in proclaiming the emperor, announcing the official end of the Han Dynasty, which lasted for more than 400 years. Immediately, Liu Bei, who had been fighting for half his life, was proclaimed emperor in Chengdu. A few years later, Sun Quan, who had reigned in Jiangdong for three generations, was proclaimed emperor. The situation of the three kingdoms of Wei, Shu and Wu was formally formed.
Judging from the comparison of the strength of the three countries, Cao Wei is the strongest, occupying the largest territory, although after the destruction of the war for hegemony in the late Eastern Han Dynasty, the economic foundation is still better than that of the south, and there are many talents;
Soochow secondly, Soochow occupies Jingzhou, Yangzhou and Jiaozhou, and there is the Yangtze River, thanks to the war in the north, the talent has been greatly replenished, and the economy is also booming;
Shu Han is the weakest, the establishment of the Shu Han just lost Jingzhou, soon Liu Bei was defeated in Yiling, only one state, although Yizhou experienced less war, the economy also has Shu brocade, well salt, etc., but the overall development is still relatively backward. However, Shu Han also has a natural danger of the sword gate, which is easy to defend and difficult to attack.
If you only look at the comparison of strength and weakness, there is no doubt that Shu Han was the first to perish, followed by Eastern Wu, and Cao Wei may dominate the world. But this is not the case, Shu Han was indeed the first to perish, and then Cao Wei, who destroyed Shu Han, was also replaced by the Sima family, and finally Eastern Wu.
All this has to mention the social structure at the end of the Eastern Han Dynasty. At the end of the Eastern Han Dynasty, due to the serious land annexation, the wealthy clan had far better strength than before, which led to their unwillingness to obey the imperial court, and the local area could even be said to be detached. The Yellow Turban Rebellion undermined the authority of the imperial court, and the localities became fragmented. During this period, the Hao clan became the main force influencing the political situation at that time.
Whether it was Cao Wei, Shu Han or Eastern Wu, it was a combination of princes and local wealthy families. For example, Cao Cao absorbed the Xun family, the Zhong family, the Chen family, the Sima family and other wealthy families, and Sun Ce and Sun Quan were united with the "four surnames of Wuzhong" Gu, Lu, Zhu, and Zhang.
There are pros and cons to combining with the Hao, the advantage is that the Hao will fight against foreign enemies together with the princes, and the disadvantage is that the Hao family may replace the princes as the new princes. This happened to Cao Wei and Dongwu respectively.
Cao Wei's political system has always relied on the Xiahou Cao clan to suppress other wealthy clans, such as the Sima clan, the Zhong clan, the Chen clan, and the Xun clan, which have actually been suppressed to a certain extent. And when the power of the Xiahou Cao clan weakens, other wealthy clans will come to seize power. Judging from the later history, Sima became a leader.
And if the Sima clan wants to further replace the Xiahou Cao clan, they need to make war achievements, and the biggest battle achievement is to completely defeat an enemy country. Relatively speaking, Shu Han is relatively weak. Therefore, Sima's first choice for the ascension was to eliminate Shu Han. After the elimination of Shu Han, the Sima clan will set out to replace the Cao clan. In the process of stabilizing the world, the Cao clan will definitely cultivate some loyal supporters, and the Sima clan needs to spend a certain amount of time to maintain internal stability, and once internal stability is maintained, it will attack the last target - Soochow.
To sum up, the struggle between the Hao clans, especially between the Sima clan and the Xiahou Cao clan, as well as the alliance of Shu Han and Eastern Wu, made it impossible for Cao Wei to eliminate any country in the short term. And after the victory of the Sima clan's struggle, they needed a big victory to consolidate their position, so Shu Han became the best choice. After pacifying Shu Han, the Sima clan needed to stabilize the interior, that is, to replace Cao Wei, and then to eliminate Eastern Wu.