Unlike other major powers, the Thousand Race Empire might not be as domineering but this only applies if you hadn't broke any rule or law that they have put into an agreement or when you are staying in Thousand Forest Continent.
The elite army of the empire is one of the most feared battalion of this world, especially since they have been baptized by numerous wars that had happened on Thousand Forest Continent and in this world.
Even the well known Tyrant Dragon Battalion is weaker than any of the elite army on the empire, Shadowslash knew this after being infirmed by Sans and Leafinia.
Since he had been traveling back to Hope City, he would spend some time learning about the current situation and condition of the kingdom, it seems that Sans and the others have been following and improving all of the advancement plan he had for the empire.