Phase I - The Prelude
Immortals of the Sphere of Energy discovered that the powers the Glantrian artifact provides to wizards drains magical energy to the point where magic's very existence on Mystara may be threatened. These Immortals decide to intervene and conspire to destroy the artifact. Their scheme would break an age-old pact with the other Spheres that forbade any direct involvement with the affairs of mortals. This causes a catastrophic schism in the Immortals' pantheon.
The spiritual patron of the Glantrian wizards, Etienne d'Ambreville (see d'Ambreville in the previous Chapter) adamantly opposes the artifact's destruction. It is his conviction that the time of magic has passed on Mystara and that it should yield before true science and technology. Magic should be reserved to Immortals only. For this reason he opposes the artifact's destruction. His opponents form the Ring of Fire, a loose alliance set against d'Ambreville and the artifact. In response, d'Ambreville establishes the Fellowship of the Star, an alliance with several other Immortals opposed to direct intervention among mortals. The two factions run into a stalemate. They cannot defeat each other and decide to fight the conflict down at mortal level.
Phase II - The Build-Up
The Immortals start building up their forces, trying to increase the number of their followers - the more followers, the more power to the Immortals and their causes. This leads to a fierce race for magical power. One after another, states, kingdoms, and empires fall under the control of an Immortal. Adventurers are sent on quests benefiting one faction of Immortals over another. Immortals of the fifth sphere (Entropy) so far remained quiet. They secretly and systematically help weaker factions. Their plan is to ensure no faction gets a cheap victory, since Entropy feed upon misery and destruction. These Immortals are known as the Brotherhood of the Shadow.
Phase III - The Great War
Immortals assembled large forces of mortal followers. Raids and local wars break out. Soon the conflict degenerates into massive campaign wars (Alphatia clashes with Thyatis, the Orcs of Thar invade Darokin, the Shadow Elves seize Alfheim, and Ethengar plunders the Northern Realms, etc). The Brotherhood of the Shadow causes conflicts to be as devastating as possible according to their plan, and quietly keeps switching sides. The Brotherhood of the Shadow becomes the leading faction.
Phase IV - The Aftermath
At the end however, the Brotherhood of the Shadow openly sides with d'Ambreville and his allies, hoping to ruin an all out attempt from the Ring of Fire to destroy the artifact.
The Ring of Fire rallies the Thousand Archmages of Alphatia and throws them against Glantri. Their bold move succeeds and the artifact is neutralised.
Although not destroyed, the artifact no longer drains magical power from Mystara. Instead, it feeds upon the evil powers of Entropy's grimmer fiends, vampires, liches, and other servitors of darkness, greatly weakening the Immortals of Entropy in the process. With fear, they now sense their possible doom in centuries to come.
Alas, the cost of the battle remains very dear to many. The Alphatian archmages are destroyed in their assault of Glantri. They were the source of an arcane power upon which Alphatia was built, and their demise causes the destruction of the arcane empire. With horror, the wizards see Alphatia's mainland sink into the cold Sea of Dawn.
Unbeknownst to mortals in the Known World, the Wizard Empire becomes a floating continent in the Hollow World, while its remaining colonies fall under Thyatian occupation.
Etienne's Immortal soul is trapped in the artifact and corrupted. He becomes a minion of the Sphere of Entropy, along with all his followers in the Brotherhood of the Radiance.
Glantri is ravaged by the war, becomes a pawn of darkness, and sinks into a dark age. Glantri and the Orcs of Thar become the new threat against mighty Thyatis. In the mean time, the face of the Known World has forever changed.