Usually, the cultural modification movement targeted at a large civilization would last for two to five generations. However, it had been less than thirty years since the Kunde Race started accepting the cultural transformation. It was still quite early to talk about letting them out.
The dynasty probably had a certain reason to do that in advance.
Han Xiao had a rough guess.
Although the Kunde Race lost, the billions of their remaining population were quite a considerable amount of manpower. Now that they were settled in the Black Star Army's territory, they basically belonged to the army. Plus, while the cultural transformation was carried out, the Black Star Army was also promoting the benefits of the army, trying to make the Kunde Race loyal and yearn to join the army.