The Cosmosphere was once a single entity within the Unknown. How it came to be is uncertain, but many suggest that it was born from the remains of a previous Cosmosphere, as part of an infinite cycle of creation and destruction, surrounded by the void.
And so the Cosmosphere was created. All of existence was contained within it, all consciousness, and all of its ultimate destruction. And the Cosmosphere was both chaos and order, good and evil, and so it began to evolve and deform within itself, eventually forming the One Realm.
Within the One Realm dwelt both life and death, and all alignments of creation. But this form too was unstable, so it warped on itself, and eventually gave rise to the Ley Field, from which all magic originates, and the Outland, a sphere of chaos.
For a while, the One Realm, the Ley Field, and the Outland were separate. Those creatures that lived and died and lived again in the One Realm had no arcane magic. Their chaos was not that of the Outland, but rather it was one of disorder than reorder in an endless cycle.
But even then, this was not enough. For death and disorder began to dominate, consuming the Realm more quickly than it could be reclaimed by life and order. And so the One Realm collapsed on itself, and its denizens cowered in fear of their world as it crumbled around them, and as they slipped into darkness.
But not all was lost, for from the destruction arose a new form. The most powerful of the beings of the One Realm were the Old Gods and their kin, who were so tied to their world that it’s death would mean their own. So the divines spent their greatest powers.
The One Realm split, and formed into the three Realms: High Realm, Middle Realm, and Low Realm. And order too was restored to balance the chaos of the Outland in the form of the Dark Paths. Around the three Realms, the spare remains of the One Realm merged and formed the Astral Plane, from which the gods influence the realms of High, Middle, and Low.