After Divine God Palace Master's Sun God King‘s mysterious disappearance, all the hideout masters automatically retreated into the underground.
The underground had been cleared out by Hellgate in secret ages ago, regardless of the occupants' species. They had all been exterminated by Hellgate's strong plague, the top-tiered experts had been secretly eradicated after Hellgate's breakthrough, and mankind's strongest organization: Elder's Hall had been annihilated.
It could be said that the underground had been emptied out under the leadership of Divine God Palace Master, and the lords of the hideouts have avoided the fight over resources with the humans on the surface. Instead, they began excavating the underground and formed an independent force to be reckoned with.