When the world first see portals and dungeons generating, humanity had no means to defend against it. It was one of the celestial beings, Setnath, that urged the others to send their aid as responsibility.
Even then, the world had already been covered in miasma from the dungeon breaks. The beasts roamed free, preying on the remaining colonies of survivors, painting the world in dark miasmas that brought nothing but death to the living.
The towers came down at these desperate times, like a holy beacon that purified the miasma around it, and gave birth to the awakening of humanity's dormant power. With the help of the tower's purifying effect, and humanity's new powers, humans slowly regained their territory and rebuild the civilization.