The War of the Wayfarers

Early Days

When the world was young, there were fewer gods. The Velen had not yet all gathered together, and the world was a very different but relatively peaceful place. As time went on, many new gods, wayfarers and wanderers emerged. The first of them blended seamlessly into the world, taking on positions that contributed to the divine workings of the world. However, this harmony was not destined to last, as one day, new gods entered the world, who would be welcomed graciously by the Velen, unaware of the dark times that would follow.

The Tragedy of Luminara

One of the middle wayfarers, Luminara, had been greatly loved by the gods. She had been friends with many of the gods, including Soreithra and Deiwos, arguably the parents of this world, but this wasn't meant to be, as during a dispute between Soreithra and Luminara about their mutual relationships with Deiwos, one they both held dear, Luminara was struck dead by Soreithras wrath. Whether rightful or not, this ended up causing the split, with different factions forming, such as the Velen and those they named the Forsaken.

Differences

One of the wayfarers that had been closest with Luminara, Trezkgal, gathered others of her loved ones, with the intention of taking revenge for their fallen friend by killing Soreithra and any who stood with her. There were multiple cases of gods switching sides, some joined to Forsaken for the sake of revenge, others simply for the sake of wreaking havoc, but the forsaken grew in power, and soon, there would be war.

The War

The war itself was not particularly long, but the clashing of gods and their titanic powers plunged the world into death and ruin. The times of struggle and chaos that followed have long since been forgotten, lost to history, but the echoes of catastrophe are still whispered about in the legends and myths of times long forgotten. In some places, there can still be seen the remnants of giant craters, locations where godly battles had been fought. Some lands even sank beneath the ocean for good, while others were raised up.

Post-War

After many clashes and great power struggles, the Forsaken as they were named by the Velen, for their attempts to overthrow them and bring chaos to their world, were defeated. Some of them were even killed, their energy scattered into the world, and now only three were left. They were not able to force them out of their world, but with their combined power, the Velen managed to banish them into the dark depths under the surface, the shadowy corners of the world, where they linger still. Soreithra would watch from within her flames, Deiwos would patrol the world from the sky during the day, and Nula would be the world's guardian in the night, and the others would aid them. Together they pledged never to let the Forsaken rise again, never to let them see the surface of the world another time.
The Velen, not wanting to repeat such events, decided together that enough was enough, and they would no longer accept new wayfarers into their world. The ones who stayed would be it, and they closed their world to newcomers, as well as they could.
The Forsaken had been defeated, but the world would never be the same. Humanity had been decimated, having suffered the most under the war, and the world was in ruins. The Velen had been forever traumatized. The world that followed was a quiet one at first. The Velen got back to their normal tasks, humanity grew older, and with each generation, they slowly forgot what it had been like.
Yet, the Forsaken, although put out of mind, were not forgotten. They kept quiet at first, for many centuries, but eventually, whispers returned of dark forces waiting to return, simply biding their time. The shadows of the past loomed over the quiet world, leaving an unsettling undercurrent beneath the surface of lost memories, awaiting the day when they could claim their revenge.

The Price in Gods

With many gods dead, and some banished, the world was a very different place. A place of loss and sorrow, at least for a while. The corpses of the fallen gods would not simply decompose though, as dead humans or animals would. They lingered, decaying, their energy still as potent as when they were alive, just without a sentient god to rule it.
The corpses of these fallen gods are called Aetherium

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Gods Killed during the war:

Fire, Death, Lights in the sky day and night, clouds of ash and dust forever covering our view of the heavens, and the thunders, louder and more terrible than anything you've ever heard. And the sound of mountains being cracked in half. Entire landmasses flooded, some to never emerge again, and with the ashen clouds hiding the sun, there wasn't a single good harvest for decades.
-Human Perspective, a story passed down from generation to generation.