After the battle with the Six Emperors, Qing Yu and the others had no intention of causing trouble for the Southern Border.
The most notable Xinglie's Battle Body from the Southern Border was lost, reducing its value significantly. Qing Yu himself was temporarily uninterested in the Southern Border's territory, as it's isolated between Daqian and Hou Qian, a remote enclave.
Moreover, the Great Witch Sacrifice should still be alive, only hidden for now.
In such a case, it's better to let the Southern Border continue to cause trouble for Daqian. On the Ling Province battlefield, although Daqian achieved a decisive victory, the Zhen Shan Army had withdrawn early, so their primary forces remained intact.
Most of those who died on the battlefield were Daqian soldiers. On the Southern Border's side, it was mainly the locust god poison that perished. Thus, even with the Great Witch Sacrifice, the Southern Border would still pose a significant problem for Daqian.
