History of Varada

Before Varada, many different worlds and planes existed in a kind of order in the universe - a Great Wheel. Countless billions of peoples and Gods lived and died in these realities for millenia, before it all came crashing down in the prophesied apocalypse. And that is where the history of Varada begins - with Leviathan, her Flood and the Cataclysm that followed.
The Great Dinner Plate (click for metaphor)

The Great Dinner Plate

To truly grasp the scale of the destruction, please allow an attempt at metaphor:
Imagine the cosmos of this old reality. The Great Wheel: in the middle there are the multiple material planes, different planets and realities. Outside them, overlapping those worlds are the Feywild and the shadow fell. Vibrant and bleak versions of those words intertwined with them. Surrounding them is the roiling elemental planes, always in flux. And surrounding them are the outer planes, each one a spoke on a wheel. The upper spokes of the wheel are the planes Elysium, Arborea, the seven heavens of Mount Celestia and so on. There is Mechanus and limbo and strange cities in the neutral outlands. Below are the Nine Hells of Baator, the Abyss, Acheron and on and on. Surrounding and connecting all of these are the ethereal and the astral sea.

Now imagine that wheel, the vast cosmos - the universe itself is lying flat on a dinner plate. The outer planes span the rim of a dinner plate, one that say, is being held. Imagine then, the dinner plate was dropped, shattering it on the floor and the shards split and cracked - some into dust, others into fragments small and large. And then imagine that the fragment that was the elemental plane of water, began to bubble and burst and overflowed until all these shards were floating in a vast sea. But the sea did not wash everything away. There was a moment when everything was at a precipice and it looked as though everything might have floated away and into nothingness. But something has kept these fragments floating together, connected by something, holding some kind of shape together.
Hopefully that wasn’t too clumsy a metaphor - a way to help grasp what has happened.

The Flood

There was a vast planar war of Gods, Titans and the very creative forces of the universe. And the war threatened to end everything - in fact it was prophesied to end. Everything was supposed to drown, the shackles on the great Leviathan were broken and water poured forth endlessly until all worlds and planes were flooded. It is also known as the Cataclysm, for the sheer destruction that was wrought. Vast alliances of gods and mortals, old enemies made friends, fought and died and failed to stop the destruction. Was Leviathan simply following the script of prophecy? Perhaps. Though the ancient legends speak that the wrath of Leviathan is one of revenge - that she rose up to destroy those that had imprisoned her at the dawn of time. Whatever the reason, whole pantheons and worlds were eaten by Leviathan, and even the most stalwart ascended heroes and Gods of the age could not stop her. But they did not drown, as foretold.

The Mercy

At the last moment, something miraculous happened. The endless wrath of the Deep Queen was sated, abated. Why? Who can say? There have been entire religions created on the subject. It is known now as The Mercy, or the Quieting. Some myths tell that a deal was struck among the deities that would come to be known as the Three Mothers, other myths speak that love calmed her heart, others still whisper that some unknown force finally defeated the terror of the deep - and that her forces now worship only her shadow. Perhaps, simply, the Mother of Water was finally finished with her terrible work. Whatever the truth, the seas calmed, and though many rifts and portals remained, the structure of the this new, unexpected world held together by some new force of magic.

Ostara

That force of magic that prevented everything slipping into the abyss of oblivion was Ostara. The Mother of Magic reached out her hands and bound the remnants of these worlds into one, fusing different seas and oceans together with network web of portals, whirlpools and maelstroms. However, this great act of creation had a terrible cost - that of her voice. She is now known as the Silent God: even the most devout of her faithful, immortal scholars or Exarchs cannot hear her will. Every prayer and spell to entreat her is met with silence. Her path is perhaps the most difficult of faiths to walk, yet her power is evident in the very nature of the world.
All of these strange and wonderful planes were now physically connected by these portals and seas. Though you may be able to sail from island to island, and even through portals to other seas and other islands and continents, everyone understands that with the right ship, the right crew, knowing the right paths through the chaos of these whirlpools and portals, even a mortal crew could reach the shores of planes that Gods claim as their domains. What becomes of them if they manage such a feat? Either they are never heard of again or they become the great storied heroes of the age. And there have been new sagas written in past centuries of mythic figures who dared to make these voyages to treat or war against Gods and secure their status as legends.

The Grey Mariner

In the chaos of this universe-ending catastrophe, there were countless deaths. Billions of mortal souls adrift in the astral sea, unable to go to their promised afterlives - and all the Gods unable to help. Leviathan devoured most of these souls, gorging herself as she obliterated everything. But as the seas settled, the souls had no way to those old planes anymore. If they existed at all, they were changed irrevocably.
And so, the Mother of Death emerged from the shadows. Perhaps she acted independently, filling the void as a necessity. Legends speak of a deal that was struck, that this new Underworld has the blessing of Leviathan. If there is a truth to be had, it is lost in the mists of time. Thus, below this new vast sea of planes and islands and new aquatic and nautical landscapes was another sea that sprang forth. Something actually more apart from the rest, though of course the legends do speak of the rare mortal who has made it there, alive. A dark, quiet, welcoming sea that stands apart in the darkness. And so these souls found their way down instead to the Silent Shore, at the edge of the Seas Beyond. Where the Grey Mariner ferries all souls of the dead. It is the known end for all mortals in this new world.

A New World

And what of those mortal people? They survived, and have come to thrive upon the seas. Through all the portals and rifts, the survivors of this apocalypse were spat out onto new islands formed from old worlds. Every nation, every island community of this world started out as a band of planar refugees, building something anew. And they have built wonders, some fashioning vast floating cities out of the wreckage of old world technology, others banding together in alliances of trade and diplomacy. And yet others use power to take and conquer - these new seas are not free from imperial ambitions or from piracy.
That is not to say that all of the old was washed away. Some planes and factions managed to maintain a semblance of their former selves. Even some of the old Gods survived, though many are new incarnations or rumoured to have been ascended mortals who took on those mantles.
And so the Wheel, shattered as it may be, keeps on spinning.