Martial Peak - Ch. 2518 - The Mysterious Hand

[MangaDex]

 

[Kaarme]

So, basically the demon realm is already devoid of life. The demon killed most of their own people and the remaining millions were transferred to the humans lands, to mostly die as well. It's pretty ironic that Yang Kai promising to grant the demon kin a new land is actually more about saving the demons from themselves than from the crumbling demon continents or from the war. The demons' worst enemy are their own demon saints, not their deteriorating environment or the humans.