I have two conditions

The powerful demonic creatures had power that far exceeded the Nirvana stage in this world, and they could easily destroy the world.

The weak demonic creatures had at least the cultivation of the spirit-refinement realm.

This caused even the weakest demonic land to have an overall strength that far exceeded the world they were in.

Fortunately, there was an invisible barrier between the demonic lands and this world.

Furthermore, this barrier could only be used in one direction.

The cultivators of this world could cross the barrier and enter the demonic land.

However, in the demonic land, even those who had reached the transcendent level could not cross the line and enter this world.

After discovering the existence of the barrier, some of the forces in this world began to plot against the demon lands.

They would start to cultivate cultivators who specialized in entering the demonic lands, hunting demonic creatures, and extracting resources.