In this final age of destruction, the two remaining Anu bombed many of the places that the Anu once built on the surface. Fearing that any leftover Anu technology – or even newly developed human technology – might be used against them, they bombed entire nations back to the stone age.
Several times, they nuked an entire city, causing radiation to poison the area for many years to come. On four or five occasions, they caused extinction level events and killed 90-95% of the human population.
It was no big deal to them.
They were crazy, and paranoid, and at war with each other.