Lucifer hypnotized Nuces & Voco, attempting to use them as sacrifice to destroy Deus because Lucifer wanted to be ruler of the Gods..
Using Nuces & Voco, he'd absorb so much energy he'd become red, he'd suddenly absorb their entire souls and lift their dead bodies into the sky forming a ball of uncontrollable power.
(Keldon made the other part) With the ball missing, and going under the clouds a MASSIVE explosion would send Heaven into a complete hellscape, with nearly all of it obliterated.
But the great abyss has been transformed, a massive explosion happened, known as the Big Bang which made the Middle World. And we are now, the aftermath of a complete failure to overthrow Deus.
When Deus found out farely quickly, he was outraged and sent the power exhausted Lucifer and the nearly obliterated heaven into exile somewhere that he will never be found, while leaving what remained under his rule.
100 Years later, Heaven is completely rebuilt and Deus now decides to goes into hell with Lucifer and who stays in Heaven.