Age of Desolation

The Age of Desolation was the time period that signalled the end of the Mythic Millenia. For roughly one hundred years the world was ravaged by a war, fought between the Blackguard Legions, who were backed by the forces of the Abyss (and some parts of the Nine Hells, strangely enough) and the gods and their servants (both celestial and mortal). Much was lost and destroyed in this time. Maps had to be redrawn, entire kingdoms engraved on monuments, and so much knowledge rediscovered (or written off as lost forever). It truly scarred the world as a whole and even though the visible injuries have faded and been forgotten, historians and scholars mourn the loss of the ephemeral to this day. And it was not only knowledge, which became an invisible casualty to the war that was waged between the dark knights and the forces of good. Mortal potential has sunk significantly afterwards. We have been rightfully restricted to only wield miniscule scraps of what we had previously (the gods were prudent in their judgement, trying to prevent another catastrophe). Even those legendary heroes of younger times are only a shadow of what their predecessors from before the Age of Desolation were. What could have ever caused such a tragedy (a good question, dear reader)? Well, history does not tell, though it likely was due to mortal folly. The little we know points towards an uprising, a rebellion against the gods. A few mortals decided to wage war on what they envied most and could never reach. How they came so far, destroyed so much and (if some sources, now deemed deeply heretical are to be believed) almost succeeded, is beyond our knowledge and comprehension now and we can only hope that it stays as such.
Addendum: There is so much unclear and missing information about this time period, that this article can at most be considered educated speculation and inferrence from the little that we do have. The only definitive facts are that the events took place over a rough span of one hundred years, that a war between the above-described forces took place, and that once the war ended, the capabilities of mortals (specifically to become powerful warriors, mages and such) greatly diminished.