War between light and shadow

“Even now, the true battle between the forces of Light and Darkness approaches. We will all be called to join, and in the face of this conflict, all mortal suffering will be meaningless.”

— The Prophet Velen

The war between light and shadow is a final, apocalyptic conflict between the Light and the Void that will supposedly take place on Azeroth in the near future, according to visions seen by the Prophet Velen and the Emperor of the Arathi Empire. The Arathi refer to the conflict as Renilash.

First mentioned in Cataclysm, the war will feature as one of the plot points of the Worldsoul Saga. The saga's second installment, Midnight, will feature the Void invading Azeroth and adventurers fighting alongside the forces of the Light to "banish the Shadow forever".

About

Velen's vision

“We must prepare the people of this world to stand together. We must be their example to rally against evil. In service we will awaken them all to form the ultimate alliance against the dark.”
— The Prophet Velen

During the Cataclysm, the draenei Prophet Velen was granted a powerful vision of a grand coalition, consisting of every race of the Alliance and Horde—all armored and armed in glowing weaponry and riding flying mounts of all kinds—along with innumerable dragons and naaru, all led by a human warrior of unclear identity clad in Light-imbued armor with a matching blade. The vision ended with the appearance of a vast and all-consuming shadow, and the army charging to meet it. Driven by this vision, Velen has ever since believed that a great war between the forces of the Light and the Void is fast approaching, and that Azeroth will be its principal battleground. He instructed the draenei to remain on Azeroth, help heal the world of the Cataclysm, and in so doing make its people strong for the future and prepare them to unite into the ultimate alliance against the darkness. For a time thereafter, Velen remained in closely guarded seclusion, not daring to waste his energy on anything save preparing for the final confrontation he'd foretold.

In one possible future, an elderly High King Anduin Wrynn, alongside Velen and the draenei of the Exodar, will lead the Light in a final battle against the Shadow.

Xe'ra

The Prime Naaru Xe'ra believed that the Void was a far greater foe than the Burning Legion, that it would take all the peoples of Azeroth and Outland united to oppose it, and that Illidan Stormrage was a hero destined to defeat it. A vision she granted to Illidan showed him transformed into a champion of the Light, leading the "legions of Light" against gigantic Void creatures on a "terrible battlefield" strewn with "mountains of corpses". It is not known if this war is the same one Velen foresaw. Either way, Illidan rejected this fate when he killed Xe'ra.

Renilash

The Arathi refer to the final battle between light and dark as Renilash. The Hallowfall expedition of the Arathi Empire arrived in Hallowfall when they were following their Emperor's "sacred vision" across the sea to fight in Renilash.