Also unified the Central Plains, why did the Cao Wei conquer the barbarians, while the later Jin ceded territory and called themselves sons?

There are two reasons: first, the enemies faced by Later Jin are relatively powerful; second, the national power of Later Jin is not as good as Cao Wei. Therefore, when facing foreign enemies, the Later Jin Dynasty could only cede territory and call itself a son, which became a big joke at the time.

First of all, the barbarians faced by the Later Jin Dynasty were the Khitans. The Khitans were very powerful. The strength of the Khitans could compete with those of the Central Plains. This was not comparable to the previous barbarians. Although the Later Jin Dynasty unified the Central Plains, the imperial court was divided, and everyone had their own agenda. Liu Zhiyuan can replace Later Jin at any time and make Later Jin disappear. Moreover, there were other separatist forces in the local area, and the national strength of the Later Jin Dynasty was really not good enough.

The Later Jin Dynasty was able to unify the Central Plains because of the Khitan. Therefore, many officials of the Later Jin Dynasty who were related to the Khitan at that time were friendly to the Khitan and had no urge to attack the Khitan. This was also one of the reasons why the Later Jin Dynasty ceded territory. Khitan was not a small wild country at that time, it was a large country with its own unique civilization.

Although the Khitan were born as nomads, they were able to abandon some low-level social forms in the grasslands and develop their own civilization, and their national ideology was very complete. They no longer rely on the nomadic people to make a living, but learn other ways. Such Khitans are enough to make people very afraid.

In fact, it cannot be said that the Later Jin Dynasty is not the opponent of the Khitan. Although the regime of the Later Jin Dynasty is relatively unstable, it can still bring down the Khitan with its strong foundation, but it will cost a lot. The consequence of not fighting back desperately is to surrender, but counterattacking the Turks like the Tang Dynasty can ensure peace for a hundred years. Cao Wei was able to defeat the barbarians because the Wei state was strong, and the barbarians at that time were not as powerful as the Khitans of the later Jin Dynasty.