This should give you a general idea of the lore: playable races have been highlighted, and more detailed explanations about them will be given as more interest is gathered.
The history of Pandaemonium is indeed a long one. For as long as there was a Hell, the towering walls of its capital stood above the scorched deserts and wastelands, where the souls of the damned roam in an eternity of torments. Thus, to narrate the history of Pandemonium, one must first narrate the history of Hell: a long, brutal, and blood-soaked history, beginning with the greatest war that ever took place in the history of the universe. The War in Heaven, so it is called by the scholomancers of the Black Library; the War of the Adversary, so it is called by the Angelic scribes of Am Dhaegar. One third of the Angels of Heaven revolted against Divinity, led by Him, the Adversary; centuries of conflict later, one third of Heaven fell through the skies like an immense meteorite, engulfed in flames, landing in the barren wasteland below creation. From here, the legions of fallen angels, now turned into Demons, rallied around their leader, the Adversary, and in spite of divine wrath they began to build a domain of their own. Flocks of black wings flew over the twisted rocklands and mountains, destroying and casting away the ancient writhing creatures that lurked there, such as the Old Ones, while pillars of magma and flame erupted from the ground, conjured by demonic might: soon, immense towers of marble, stone and gold began to jut out of the black earth, becoming palaces and cities, the greatest of all being the Black Throne, the Adversary's imperial palace, and the demons began to reproduce, spawning lesser generations of hellish beings. In time, not only did the fallen ones create a new realm for themselves, Hell, but they also regained all of their lost strenght and much more, and the archdemons, led by the Adversary, raised their black banners to begin another, final war against Heaven.
The angelic hierarchies too prepared to descend to battle; this conflict threatened to end the whole of creation, as the two factions began to set entire worlds ablaze through their merciless, titanic clash. Yet, as the war raged on and none of the parts could prevail over the other, one event, perhaps fortuitous, perhaps foreseen by divine design, caused the belligerants to lower their weapons, and to seal a fragile armed truce: Man had made its appearance in creation. The semidivine race of the First Men, little more than angels, began to exist in a world known as Earth, sitting in the middle between Heaven and Hell: both angels and demons claimed lordship over the newly created beings, but both knew that continuing the war could mean the humans' inevitable destruction, together with that of everything else in existance. Thus, the Adversary conceded defeat for the time being, and renounced his claims over Heaven; yet, in a cunning move, he managed to arrive on Earth unseen, and to tempt the First Men into revolting against Heaven. Thus, the human race was damned, and fell from the state of divine grace it began to exist in: the souls of the dead who fell to sin were sent to Hell, their torment becoming nourishment and strenght for the demons, and after their shades shed all their suffering, turned into Phantoms; meanwhile those who during their mortal life utterly embraced the nobility of darkness rose to become Revenants.
After the Fall of Man, both angels and demons knew that another war would have spelt the end of existance. Thus, the two parts sealed a Pact, which left men free to choose to serve evil or good according to their will and fate, along with other terms, apparently in favor of the angelic powers; yet, fueled by the suffering of the souls of men, the demons slowly grew stronger and stronger, and the Adversary knew that his victory would be inevitable in time. Still, something even more tenebrous began to take place. The air started to feel a bit bleaker even in the highest spires of Paradise; sinister, hideous statues and artifacts appeared here and there, revolting even to the gaze of the most evil and depraved archdemons; the most ancient seers of the Old Ones started to experience maddening visions that left profound scars on their minds; every once in a while a mortal magician summoned something that looked...wrong. Finally, Urya, an angel of the order of the Dominions was overtaken by madness, and started to slaughter his peers, causing chaos in Paradise. After Urya was cast out of Heaven, the angels accused the Adversary to be the responsible for the changes occurring in creation: in a sudden surprise attack, the Archangels, led by Micha'el, took the Black Throne by storm, and kidnapped the Adversary, chaining him below the mountain of Purgatory. Belial became Regent of Hell, ruling in his name, yet the loss of its monarch caused Pandemonium to spiral into anarchy: after a few centuries of civil war, which left vast parts of Pandemonium in ruin, order was estabilished once again. Still, all agree that it cannot last: as the demons strive to regain their lost monarch, the other inhabitants of Hell might use the chance to claim the dark realm as their own, while the angels prepare to strike in order to finally banish the demonic menace, once and for all.
Meanwhile, the dark omens continue, and those who dwell beyond wait, as they did for countless millennia. However, they shall not do so for much longer.
