Bab 2171: "Isolating The Abyss" 

However, among the various ways to become a hell demon, maybe because the previous demon king was influenced by his elf wife or something, he also had several strange pieces of information related to the whole abyss. 

Several generations of abyss demons were born in the closed abyss, barren and with almost no resources at all. 

Those born stronger could actually tear open dimension to go out of the abyss, but no matter what, because of the seal, they could only go to other dimensions rather than coming to this world. 

It was like the space tunnel between this world and the abyss was blocked by a door, and other dimensions' paths were not blocked by a door. 

Those demons used the resources in other small dimensions similar to their abyss world to grow stronger to leave this abyss world forever, successfully washing off their inferior bloodline and becoming a hell demon.