In the beginning, was just Ao. The one before time, before space, before life. Eternal was their slumber before they awoke, for time did not exist until they awoken.
This shows the creation of the universe, and the major events that followed leading into the current era of existance for the multiverse. Knowledge of this is limited to extreamly few in the multiverse.
The First Era of the Universe, when the Celest's ruled over existance, and were the most powerful Celestial beings. They created the Divine, and together with the Divine created the Celestial Planes.
In the beginning, was just Ao. The one before time, before space, before life. Eternal was their slumber before they awoke, for time did not exist until they awoken.
Ao then harnessed this power of creation, and formed the first true world, Celestia. Celestia was a beautify utopia, combining powers all four elements, and empowered by the Positive energy with in the Inner planes.
As the powers of pure creation seeped from the Astral sea through the Inner planes from the Higher Plane of Celestia, the primordial soup of elementals began to form into a great plane of Elemental Chaos. This the Plane of Celestia could witness, and cared little for what was happening there for it was far away, and they had plenty to entertain them selves with.
As the energy of the Astral Sea seeped through the Elemental Chaos, some it began to interact with the Negative force of the Inner Planes. This formed formed a new realm all to itself, one of darkness and Evil, but much in reflection of Celestia it was orderly, and not in state of flux like the Elemental Chaos Plane, but rather one of order, almost as a reflection of Celestia.
The Celest, not content being alone after many centuries, and growing bored of just each others company, decided it would be best to draw power from the Astral Sea, and form new planes of Celestial Existence, as well as new beings. These beings they formed they called the Divine. Beings of Power, that they imbued with aspects of existence the Celest had discovered.
The formation of the many Celestial races in the upper planes, leaked a new kind of magic through though the Astral Sea, which seeped first into the Plane of Elemental Chaos, which formed the primordials who gave first shape to parts of the Elemental Chaos using the power of creation from the formation of the new Celestial Planes.
After this the power of Life filtered what was left into the bowls of the dark realm of Hell. This gave birth to the first Devils, who jealously sought dominion over all the realms, being heavily influenced by the negative energy in the Inner planes.
The creation of additional planes also had an effect in the Lower Plane making 4 new Planes of existence. Forming the Planes of Acheron, Gehenna, The Darklands (now the Gray Waste), Carceri.
A fight, started by the Celest Gruumsh, that led to the creation of the Seldarine from the Blood of Corellion another Celest, and the Oriki from the cut flesh of Gruumsh. This battle was the first combat between the Celestials, and it was gruesome fight. In the end, Gruumsh lost an eye, and the other Celests intervened, to prevent the two from ripping creation apart.
The Seldarine who formed of Corellion and followed in their wake and shadow, eventually caught the attention of Corellion who weakened from the fight with Gruumsh, who then paused the endless wandering, and sat with them to learn more about them.
The Abyssal Shard arrived in the multiverse through its own magics from collapsing ancient universe, one never apart of this one. This Shard held the collective power of the dark race which had conquered and ruled this other multiverse, and sought a way to escape the inevitable collapse of their universe.
By this point, there are essentially 18 planes of existence and the Astral Sea; Baator otherwise known as Hell ruled by Devils, The Abyss which is the endless pit of Demons, the 14 planes created by the Celests, The outlands that exist between the Outer planes, and the Great Elemental Plane ruled by what is left of the Primordials. Conflict grew between The Celests, Demons, Devils, and Primordials, and eventually broke into all out war.
The War had broken more of the Great Elemental Plane, and this divide grew through even the Astral Plane, until it formed its own new level of existence, now referred to as the Material Planes.
Eventually, after long back and forth wars, The Treaty of the Mechanus was signed. In which The Planes of Mechanus and Limbo were declared the boundaries of the upper and lower planes between the Celestial beings in the Upper Planes, The Devils and Demons in the Lower Planes, and the Elemental Planes will remain held by the Primordials. The Material Plane remained a space for any who could claim it.
Seeing the Seldarine and Oriki and Orcs, other Divine wished to have their own Mortal races, and found ways of forming them. Many of the Divine were growing uneasy about the Material Plane, and even though it was filled with horrors, would send their mortals into that realm to try and claim space for their Lord in that realm. The first was Aoura, who filled the Divine realm of Arborea with all kinds of creatures, and allowed them to spread to anywhere in the realms where they could. These were the first animals.
Troth, the wisest and most curious of Celests created the Outlands which stretch between all the upper and lower planes, and even borders into the Astral Sea, the Material plane and Elemental Planes. From this massive landscape Troth observes the known universe, and meditated on the plan of Ao.
Lolth, who among the elevated Seldarine was most respected by the others, spent time looking beyond Arvandor into the material plane. There she saw how mortals made marks in the world, made changes. She was convinced that the Seldarine could do better then any mortal race, and saw great potential. She convinced many others to abandoned the ever shifting form, and took a singular form. Thus the Elves were born.
The Divine Maglubiyet spent his time conquering other Divine, destroying them, and taking their mortals for his own, this formed the Goblinoid species.
Maglubiyet, and his Host of Goblinoids, were confined to the Archeron Plane, but he still sends his Goblinoids into the Material plane to conquer and expand his control, and create new Goblinoid souls.
Having seen enough of the Universe, and growing tired, many Celests had grown tired of the universe, having great knowledge and power, they can direct the very flow of existence in their realms, and nothing surprises them any more. The Material Plane had become another space of fighting to them, and it worried them that the corruption of the Lower Planes would continue to spread until it consumes them.
This Era was marked by the suffering caused by the retirement of all the Celests that had not been judged worthy, leaving behind the corrupted Celest behind to be the most powerful rulers.
It did not take long, ready to be reunited with Ao, for all Celests that Troth determines worthy the transition has completed after only a decade. The Celests who are refused become very jealous, and instead begin work on rebuilding the whole of the universe to their own wishes and pleasure, which due to the corruption they had suffered in the Lower Planes during the War, was very different. The Divine became Slaves to the Celests. Troth, choosing still to observe existence remained within the Outer Planes, and continued to judge and sort the souls, as suffering began to abound.
Primordials asserted to the Old Ones, that the prime plane of the Material realm was theirs, as it was broken from their plane. They contested that the Divine should keep to Feywild and Astral And ethereal plane, the Devils and Demons Shadowfell,, and prime plane should be for the Primordials.
The Old Ones, wishing to consolidate their power they planned to reshape each of the upper planes to reforms a single endless plane of their version of perfection. To this end the tasked each of the divine and there mortals with recrafted portions of the planes, And to do so they required that none draw power from the Astral sea, for the Old Ones did not want to reduce the distances between realms. This was an arduous process that took many mortal lives, and would take millions of years.
The Dark Celests had forced the Divine to abandon the Material realm to serve them. The Elementals, Devils, and Demons take the mass of the Prime plane. Many mortals are forced to submit to the rule of these evil creatures, and this was preferable then to dwell with their gods in the Celestial Planes in many cases. But the Pain and Suffering was spread not just there, but across all realms, as the celestial realms grew darker and darker.
Troth provided a boost of power to raise Pentharion above all Celests, with the use of his own power. Together, Pentharion, Corellion, Pandora, Agethis, Aoura and even Gruumsh managed to unite the other Divine, and Celestial beings together to overthrow the Old Ones.
Pentharion and the other Divine with the other Celestial beings, and the Mortals still dwelling began restoring the Celestial Realms. They were allowed to pull from the Astral Sea, and the work did not take long to restore, though the distance was between realms was slightly reduced to do so.
After the Divine had restored the upper planes, Pentharion began the next stage in his plan for ending the Dark Celest Era, in honoring the Treaty of Mechanus and the Infernal Pact, he declared the Primordial Pact illegal. Instead he declared a new balance upon the material realm, ordering that the primordials to be removed from power, and banished back to the elemental planes, and that the Material world would reflect the balance between all realms.
The Celestials begin to retake ground within the Prime Plane, and united again with several mortal races to push the Primordials out. They even managed to gain alliances with several of the Elemental races in exchange for being allowed to continue there own governance of their territories.
When the divine returned to the material plane, Apollyon found the tieflings worshiping Devils and Demons, and they refused to return. In his anger he cursed/blessed a small few who did return to him, along with some Drow and mortals that now inhabited the lands after fleeing the prime plane.
During the Primordial War for the Prime Plane, Eldridth was overlooked at first, until it tried to free itself, which inspired Gaia, Vashnar, and Phaestus to come to the aide of the enslaved races there from the Primordial Azar who had made a deal with Asmodeus to share the world with Tieflings, and thus the Devils they serve.
The battle against Azar and the Divine was almost bare even, especially after he turned against Law and Order, and Embraced a Demonic power. In the end, Clementis helped the other Divine Seal Azar away, and Aegis arrived breaking the world, and brought an army to defeat the hordes of Orcs, and together they fought to free the newly formed continent of Aygess.
Once the Primordials were no longer on the Prime Plane, and cast back into the Elemental Planes, Pentharian made the Prime Decree, which marked the end of the Dark Celestial Era, and the beginning of the Divine Era.