The beginning of the Mortal Era and the final act of the Dawn Pantheon, sealing the Prime Material Plane from their direct and physical intervention.
After witnessing the devastation brought about by the Dawn War, the good aligned deities realised that the only way the world could truly flourish would be to lock themselves away for eternity. Led by the Goddess of Knowledge Ioun, they began creating The Divine Gate. The only truly difficult aspect of the plan was finding a way for it to impact upon every deity, because as untenable as the war had become, the idea of leaving the likes of Bane to rule over the mortals was far worse. In the end, it was the god Asmodeus who managed to convince the other deities to willingly accept imprisonment, by pointing out that each deity could form a new plane entirely under their own power to do with as they wished, while still manipulating events on the Material Plane. The strongest of the gods leapt at the opportunity to create a perfect plane in their own image, and the weaker gods were no match against the united anger of Pelor and Asmodeus. And so the gods retreated, and trusted in their subjects to wage war in their name.