You should know that just the presence of the three lesser aristocratic families from West Outer Heaven has already been causing them headaches. If Kyushu were to attack en masse, eliminating the Demon Clan would be almost effortless.
However, such thoughts seemed implausible to Cheng Ziang. East Prosperity Nine States, similar to ancient China, were conservative, tending to their own land and not apt to expand outward. The wars with West Outer Heaven had already proved this fact.
To put it bluntly, if the Dongsheng Empire were to expand, it would move north or west, or even south to invade Fengyu. But it was highly unlikely to carve out pockets of territory in West Outer Heaven.
The three aristocratic families migrated to West Outer Heaven only because they were oppressed in Kyushu. If they had a choice, they would have much preferred staying in Kyushu rather than venturing into unfamiliar territories.