Geological / environmental event
The Planar War begins and Ezzoal releases the Flood of Primordial Waters.
In the time before the Flood, there was a plethora of pantheons and gods to fill them. The most ancient of these beings were the gods of order and chaos. These gods were the original architects of the Material Plane. The gods of order created the planets, physics, time, and landscapes. The gods of chaos filled these worlds with life and gave life agency and free will. At the heart of the Material Plane was Phoenix, a planet that lay nestled on the back of the Primordial Goddess Ki.
Phoenix was a world of invention and innovation, its ability to balance technology with the arcane arts was unparalleled. Every continent was filled with people of all kinds. Cities towered high above the ground. The mortals did not know sacarcity, they had access to anything they needed.
As the Material Plane's mortal population spread, Chief Overseer Rovius desired for a means to categorize mortal life with more structure and dictate their fates. He worked alongside Overseer Tamiios, Overseer Treald, Nidra, and Exarch Lanua to solve this problem. These five gods created a tome that cataloged the fates of mortal life; every decision a mortal would make across the course of their entire life was written out and decided.
When Rovius presented this tome to the gods of chaos as a tool, Zuva took immediate offense to it. Life was the responsibility of the gods of chaos. In Zuva's opinion, this tome crossed a boundary. Zuva took the tome and transformed it into a mockery of the tome's original intent: the Tablet of Destinies. The tablet fractured the lives of mortals across even the tiniest of choices; this crafted a vast and confusing multiverse of possibilities.
Zuva presented the Tablet of Destinies to the gods of order. The gods of order reviled the item. The tablet was a mess of both order and chaos, it was viewed as an isult. The tablet also unlocked the door to the multiverse, a new frontier that the gods were not ready to explore. They were quick to hide the Tablet of Destinies before it could cause too much trouble and dismissed Zuva from their domain.
On the Material Plane, a wizard, who would later be known as the Penitent Man, received an anonymous order from Utopia to create a powerful weapon. The wizard returned with a firearm, the first of its kind. Zuva was later found dead with a bullet in his skull.
Ezzoal, queen of the gods of chaos and wife of Zuva, blamed the gods of order for Zuva's death. The alliance the gods had maintained for so long was now forfeit. Ezzoal smashed the borders of her demiplane, the Abyss, and released a flood of primordial waters across every realm, including the Material Plane.
The Flood washed over everything on Phoenix and submerged the entire planet. The land was drowned in a sea of monsters and chaos. Even drinking from the primordial waters was dangerous. Consummation of the liquid tied one to Ezzoal herself, and they would forever be plagued by visions of the Abyss where she dwells.
The scarce few survivors of the Flood were forced to live on massive arks. Most records of life before the Flood were completely lost in the storm. The only remnants are glimmers of a fantastic realm with impressive technology.