For a long time, there was no exact written information. Why did Sima Qian say that Huns were descendants of Xia Dynasty?

Sima Qian must have seen the relevant historical materials when he said this. His basis is the historical materials he saw. As for the specific content, we don't know now. We can only speculate from his description. There are two bases: First, Chunwei, the ancestor of Xiongnu, is said to be Xia Houshi; Second, the Huns gradually migrated from the Central Plains to Mobei.

According to Sima Qian, the ancestors of Huns can be traced back to a man named Chunyu, who is a descendant of Xia Houshi. So where did Xia Houshi come from? This is about to talk about the legendary first unified dynasty-Xia Dynasty. The royal family name of this dynasty is Xia Houshi. Therefore, Chun Wei, the descendant of Xia, is a direct descendant of Xia royal family. In this way, the Huns are naturally descendants of the Xia Dynasty.

But Sima Qian's evidence is not only this, but also a little weak evidence. That is to say, the legendary Xiongnu originally lived in the Central Plains, but with the rise of other forces in the Central Plains, such as Shang and Zhou, they were forced to migrate north and west. Coupled with the characteristics of nomadic groups living on weeds, they moved farther and farther, and it was not until the time when Sima Qian lived that they moved to the bitter and cold Mobei area. If this legend is true, then the Huns, as descendants of the Xia Dynasty, are naturally credible. After all, their ancestors lived in the Xia Dynasty.

These two factors may be the two bases that Sima Qian refers to when recording this history. But in the end, I have to declare again that in Sima Qian's time, historical materials were much richer than today, so it is very likely that there will be other basis for his reference.