In the beginning before God created the earth and before humans created Gods and before Lucifer became the Devil and corrupted the earth, the Heavens was peaceful. The glory of God was full and hell did not exist.
From where did corruption begin and why did God allow it to get to this point is a mystery within the mystery of every existence.
When the angels fell they created corruption as they mixed that which was once good but now evil with that which was chosen to serve the Almighty creating a race of people humanly but not quite human which was closer to heaven as it was closer to hell and the people worshipped them forgetting God who then forgot them, they are the Anunaki and this is Parabellum.
Some say God is kind and merciful for it could've been worst others say he's cruel for what he allowed to be.