During the reign of Emperor Wu of the Han Dynasty, the Huns were defeated. Why don't you take the princess back?
In fact, the princess of the Han dynasty married in the past, and if she gave birth to a child, the child became the emperor of the Huns. That would be very beneficial to the Han dynasty, but, similarly, if the princess returns to the Han dynasty. And bring back the children he had with the Huns. The princess is noble, and the children can't be civilians.
But the rulers of the Han Dynasty would never allow their royal blood to be impure. Another fact is that in ancient times, married daughters were just spilled water and there was no reason to get them back. If the married princess is taken back, this princess will live in Xiongnu for a long time. May have special feelings for the Huns.
This is very unfavorable to the rulers of the Han Dynasty. After all, the Huns and the Han Dynasty were hostile at that time. In addition, although many princesses in the Han Dynasty married Huns. But there is no Xiongnu princess who married back. The emperor of the Han dynasty hoped that the children born to the princess of the Han dynasty would become Xiongnu emperors, but he did not want his royal lineage to be polluted by Xiongnu lineage. It can be seen that the Han Dynasty attached importance to bloodline.
Then a princess who marries a Hun becomes a Hun. Therefore, the Han Dynasty would never take back the married princess.