The Archangel Michael--who had counted himself among the Peacemaker's ranks--began receiving terrifying visions of the Inferno opening and releasing the demon hordes. The Inferno had been a maelstrom of terrifying power before that had corrupted seven of the most pure angels and gave rise to the Seven Demon Lords. They had been defeated, and the Inferno was made their prison. For hundreds of years it had remained shut, but the previous battles with the Royal Knights and the Amatsu-Mikaboshi had weakened the locks, and the demon Mephistopheles sought to break it open completely.
Gathering the Peacemakers, Michael led them against the demonic trickster, but they were thwarted at every turn. Mephistopheles called upon the Four Horsemen to pave the way, and cast a spell that exiled the High Council and almost all other gods from the main plane of Theros [the name of the Digital World]
Alone, there was little the Peacemakers could do to stop Mephistopheles from succeeding. He cracked open the Inferno and loosed the Nightmare Soldiers onto the Digital World. Then, as demons that had lain in torment for hundreds of years were free to scour the world, Mephistopheles descended into the Inferno to release the Demon Lords themselves. All but two of the Peacemakers gave chase, hoping against all hope to prevent him from breaching that final circle and freeing Lucifer. The two that remained, the last of Theros's gods, chose to instead stand with the remnants of the world's defenders and stem the tide of encroaching demons.
In the Inferno, the Peacemakers faced naught but disappointment and further trials. Confronted and tormented by visions of their failures and darkest moments, the Inferno itself sought to twist them from their noble path and ensnare them forever. All the while, Mephistopheles freed the Demon Lords. One by one they rose, billowing terrible black-and-red flames. In the end, the Peacemakers failed. Lucifer, First to Fall and Last to Rise, awoke. He devastated their ranks and ascended from the pit to lay claim to the world of Theros.
It is in the hands of the demons now. Theros belongs to the Nightmare Kings.
The Peacemakers emerge from Hell to find the world in tatters. For them, it has been but a matter of hours--a day, at the most.
For the rest of the world, it's been six months since Lucifer rose. Six months since the Peacemakers were last seen. In this time, the Nightmare Soldiers have scoured the Digital World, slaughtering all those who resist; all those who fail to bow their heads to the Nightmare Throne.