Four Empires on Four Corners

the region of Yindu has been plagued by a prolonged state of conflict and disunity, spanning nearly four centuries. 

Throughout this tumultuous period, no single ruler or power has succeeded in unifying the fragmented land. 

Aeryon recalls from the book that even during the formation of the Three Kingdoms, Yindu remained divided.

The brief mention in  the book of a prince from the Yindu region meeting with the Prince of the North in the Great Steppe offers a window into the ongoing lack of unity in Yindu. 

If such a meeting occurred during the time of the Three Kingdoms, it implies that Yindu is still a region divided among multiple rulers and powers. 

From this Aeryon could make the conclusion that Yindu was not united even till that point. 

The geographical separation provided by the mountain range between Yindu and the Great Steppe has indeed contributed to the relatively low level of conflict between the two regions.