The obsidian serpents and one of them even beginning the evolution process to a flood dragon, who knew how many other dangers the Deer Mountain Range hid?
The territory was as large as a rank 2 empire and in certain areas, it was just as rich. But even then it was filled with countless dangers which was why despite the Deer Mountain Kingdom calling themselves lords over the territory for tens of thousands of years, they never had full control of it.
They did try it once, but it ended in their complete loss, and their foundations got fractured so they dared not try it again.
Yang Qing was slightly worried about what dangers lurked in the area. Xi Si's report gave him much-needed relief and as for why they didn't do it earlier, Yang Qing could more or less guess it had to do with manpower and also the nature of the Deer Mountain Range, more specifically its inhabitants.