The Offworlders' War is the name given to a two-year conflict between multiple diverse factions for control of the Offworld Gate and ultimately of Caraonis itself. Events leading up to the climax of this war were chronicled in the player campaign "Convergence of Worlds".
The conflict began as a scheme hatched by Thaeris Lacótian, former Bladesingers' Guildmaster, to allow an otherworldly insectoid race known as the "formians" to overrun Fylcordia, in exchange for control of Ferytia and Takharas. He recruited the aid of Cardinal Mordecai de Lanitoth, a human priest living near Arlyndell, and a little-known group of radical druids calling themselves The Protectorate. The Protectorate's objectives served as a distraction to the authorities in other nations while Lacótian and de Lanitoth focused on accessing the Offworld Gate and opening it for the formians. However, the formian invasion was only a means to a further end; their primary objective was the resurrection of the warlord Tyrillian Sarchas, who, so they thought, would lead a superior army of ex-Eoncordian warriors against the formians, driving them back off of Caraonis and leaving three continents under their control.
The formians, for their own part, never planned to honor their agreement with Lacótian, and fully intended to overrun all of Caraonis, claiming it as a safe base of operations, out of the reach of other planar powers. They amassed an enormous invasion force — outnumbering the army gathered on behalf of Sarchas by over a hundred to one — just outside the Offworld Gate, waiting for it to be opened for them.
Tyrillian Sarchas, having been killed in the War of Violet and Silver, had become a demon of significant standing in a conflict known to offworlders as the "Blood War". When Lacótian and de Lanitoth attempted to resurrect Sarchas, their ritual failed to return his soul to Caraonis, but did succeed in reminding Sarchas of his former life. He used the abilities of his most powerful minions to contact Lacótian on Caraonis and arrange passage for himself through the Offworld Gate when it would be opened for the formian invasion. Once so arranged, he began pulling select forces away from his eternal conflict with the devils as the start of a demon army which would allow him to control Caraonis as a safe haven from planar attack.
Sarchas's most bitter personal rival in the Blood War was a devil who used the name Hellwalker. Having been informed of Sarchas's plans by spies, Hellwalker managed, with great difficulty and tremendous sacrifice of minions, to breach the Great Planar Barrier to establish a portal into Caraonis within Cael-Daro, the ancient volcano at the center of Ferytia. The dwarves of Pyrithgârddin discovered the portal and summoned the mages from the nearby Tower of Sorcery to investigate. The mages, duped by Hellwalker into thinking that the portal accessed the Elemental Plane of Fire, and thus seeing the portal as a rare opportunity for research, helped him to stabilize the portal as a permanent breach of the Barrier. His goals achieved, Hellwalker and a legion of his minions flooded through the portal into Caraonis, and travelled immediately to Eoncordia, to intercept Sarchas and destroy him.
Lacótian had no idea how badly his plans were falling apart outside of Caraonis, because they were also crumbling from within. Two groups of adventurers were systematically hunting members of the Protectorate and disrupting his network of spies and double-agents all over the world. His only lucky break was his encounter with the Golden Wing, flagship of Yarvothas, pirate-king of Tyrillia. Yarvothas had brought the Tyrillian Corridor Gate on board, attempting to take it to Takharas to establish a foothold for a military coalition seeking to put down what they thought was only a rebellious remnant of the Eoncordian military. Lacótian's flagship, the Stiletto, encountered the Golden Wing just after it had been ravaged by a magical typhoon, and destroyed the Tyrillian ship, sinking the kingdom's Gate in the eastern ocean. This distracted the adventurers leading the counterinsurgency long enough for Lacótian to reach Takharas and prepare for the arrival of the formians and Sarchas.
All five factions — Lacótian's armies, Hellwalker's devils, Sarchas's demons, the formians, and the coalition of allied counterinsurgency forces, converged on the fields of Eoncordia between the ancient city of Sipôl Extíra and the original Tower of Sorcery where the Offworld Gate had been "sealed". When the Gate was finally opened, the formians and demons were already at war with each other outside the Gate. This conflict spilled onto a battlefield on which Lacótian's forces were already being torn apart by Hellwalker's devils. The magnitude of the conflict brought an unexpected sixth force — legions of dragons, previously thought to have left Caraonis in ancient times, suddenly appeared to join the battle. By the time the coalition arrived, the battle had already been raging for days. Their arrival turned the tide of the massive conflict like a breath of wind toppling a house of cards. Hellwalker and Sarchas killed each other; Callon Derisian defeated Lacótian, his former tutor; the bands of adventurers fought and killed the formian queen.
When the battle was finally over, tens of thousands of creatures from three outer planes, countless doomed soldiers from Lacótian's outmatched armies, and seven ancient dragons, littered the fields of Eoncordia. The Temple of the Dragon was emptied of its priests of Chrótemjin to deal with the wretched sea of dead. The site, which had been the final battlefield of three world-shaking wars, became known in folklore as an accursed, unhallowed ground, as fearsome as Necantyr Forest and deadly as the Eye of the World itself.
A group of the adventurers at the forefront of the counterinvasion army, led by Callon Derisian and Garon Weaver, took the Offworld Gate Key and left Caraonis, to find out just what lay beyond the Gate, and to attempt to seal it off forever. They have not been seen or heard from since that day.