The Azure Flames is the agreed-upon name for the global disaster that destroy the Old World and created the current world, from which sprang new and better forms of Mankind as well as allowed other species to emerge and either co-exist with Man or contend with Man for ownership of its homeworld.
It took some generations after the fact to fully collect what happened, but now we know how the Azure Flames came about. The Old World suffered for many generations under the yoke of an invisible empire of evil Men, beholden to powers not fully understood then, who used their knowledge and power to ensnare the minds of their brothers and exploit them in great and terrible acts of human sacrifice masqueraded as wars and disasters to conduct rituals of sorcery unnoticed by the ignorant and brain-washed populations.
To keep the chance of discovery within control, they created false conspiracies to confuse would-be enemies and ensnare would-be rivals, but these generational cultists lost control somewhere close to the end and the fakes became rival interests united by a mutual hatred. The wars and disasters increased in frequency, but decreased in their potency, so the cultists has to cope by working around their errand minions.
This hubris led to their undoing and the destruction of the Old World. On a date that all--even the masses--knew to be portentious and of great significance both of these conspiratorial networks simultaneously conducted their greatest schemes to fruition. On one hand, all of the cultists led ceremonies at places of great power coordinated down to the second. On the other, the rogue minions set on nuclear weapons that obliterated the ten highest-population cities on the planet in an attempt to start World War III.
Both events climaxed simultaneously, with the result that the millions of deaths powered the ritual magics and overloaded the cultists' ability to control the power unleaded by the minions. In a wave that swept the world, a ground-to-space wall of blue-white fire scourged the planet and reduced all of the Old World to ashes while leaving most of the planet quite habitable; the cities, one and all, disappeared (as ruins, or otherwise) and most of Mankind dies screaming (soon to be the undead horde enthralled by The Necromancer) while most of those surviving find themselves changed somehow.
Today, long after the conclusion of the Wars of the Damned and the fall of the Empire of Man, we can look back at that post-apocalyptic age and be glad that it wasn't us; we also are grateful that the form that Mankind took in the Old World is no longer- all the horror of that age was to ensure that this extinction took place, and we that arose thereafter did so untainted by that decadent and corrupt forerunner.
Sure, we may look like the men of old, and many of us live and die as they did, but we are not them. We are not as limited as they were, nor as susceptible as they were to corruption, and we have both the heroes and villains of that terrible age to thank for we the new breed of Mankind that are now the light of Civilization amongst all of time and space- we that brought the best part of Old World imagination to life, once we mastered the science that made the comprehension of psuedo-life possible.
Our world could not exist without the Azure Flames clearing away the diseased Old World. Be grateful, for without that destruction our creation would never exist.