The creation of the Seal

Era beginning/end

The Demon Lord begins his reign

While the Gods pursued agendas on the other Planes, the Demon Lord brought his forces to the material plane and sealed the plane from the rest of the multiverse. Dramdaus set about conquering the material plane and forming it in his image.   At the very beginning of the Demon Lord's reign, all portals to the outer planes were sealed off severing the link between the gods and their followers and creating what was known as the Sealed Taint. After sealing the planes, the Demon Lord went about killing off every Celestial that he could find and trapping their souls in the great gem that powered the spell sealing the material plane off from all others. Around one hundred celestials survived the cleansing. They went into hiding, biding their time and working behind the scenes to undermine the Demon Lord's rule.   With their followers cut off from them, the gods were no longer able to draw power from those loyal to their cause. Thus weakened they fell prey to the Demon Lord as he traveled the outer planes and slaughtered the pantheon, entrapping their souls and power in the same gem that powered his seal. After a time the gem became known as the seal, sharing the name with its effect. The souls of every vanquished enemy of the Demon Lord were placed within the seal to feed the spell severing the planes.   When his cleansing was done, only three of the gods still lived, the All High, the demon lord's father, had never drawn power from followers and as such was not weakened by the Seal, while Arun and Tork still slumbered on the material plane.   The Sealed Taint was a consequence that possibly even the Demon Lord hadn't predicted. With the plane completely sealed off from every other, no one ever left, not even through death. Fully half of the planes inhabitants were turned into some kind of undead within days of their death, most of the rest were turned into planar petitioners or some other kind of native outsider.   In the almost three thousand years that the Demon Lord ruled, this lack of any souls leaving soon led to the plane becoming rapidly overcrowded. This overabundance of souls led to the creation of many cults to the Demon Lord which ritualistically practiced sacrifice, sending the victim's souls to be placed in the seal.