In the year 582 CY, it started in the north with the barbarians in the Hold of Stonefist. There was a tale going around that all but one of five magical swords called the Swords of Corusk had been found. When the final one was located, a rumor began that a great god would come and lead the men of the North to greatness. The sword was never found, but nevertheless a man named Vatun suddenly appeared, out of nowhere it seemed, and claimed to be this great god. He then led three tribes of barbarians against Stonefist Hold. Stonefist was taken rapidly, and suddenly the commander of the fortress changed his allegiance. (It's believed this was done via the Art.)
In the same year, under the leadership of Vatun, the Fists moved against and occupied the Duchy of Tenh. No one rendered aid as a result of the priggish Suloise decent typical to most inhabitants of the duchy. Apparently due to their prior arrogance everyone sat back and smiled as they were invaded. Soon though, Vatun made a mistake and his gathering of hordes collapsed. He commanded the barbarians to invade Ratik, but they flatly refused. There had been a long standing alliance between the barbarians and Ratik against humanoids native to the nearby Bone March. Doubt began to grow as to this Great God of the North, Vatun. Of course the barbarian's great god was none other than Iuz the Old in disguise. But Iuz no longer needed them - he was ready to move on into the east and west.
Iuz moved into the Horned Society with the aid of fiends running through the streets of Molag. He seized control and began to rule from that city. Furyondy took notice at this point and, in a near panic, craved an alliance with the Shield Lands. Afraid that Furyondy was trying nothing more than a bold attempt at annexation, they refused. For their folly they fell to Iuz's main body of troops, along with the adjacent Bandit Kingdoms.
Furyondy held its eastern border in CY 583 with the Battle of Critwall Bridge, while in the north Crockport was taken after a massive force of humanoid mercenaries moved into the capital Chendl. Many battles still waged and finally it was that Furyondy and Iuz were drained. Then suddenly the Great Kingdom struck out with great masses of troops establishing multiple new fronts.
Even though Nyrond was wary of Aerdy, they moved in and attacked at the Fists that were rampaging through the Duchy of Tenh. Once there they found they couldn't stand against them long and that their suspicions about Aerdy had been correct. Aerdy moved south and southeast into the Iron League, west into Almor and inevitably toward Nyrond. During the winter of that year things settled a bit. The Iron League allied with Nyrond but then a secession split the League. A Prince of the Lordship of the Isles was replaced by a cousin who announced his favor of the Scarlet Brotherhood. Also at that time, Nyrond had to watch out for the Bone March that began threatening it, as well as Ratik. Things seemed more settled in the west, but Iuz had been far from idle. The Old One was welcomed in Ket, whose leaders saw chances to annex Bissel. Once spring came in CY 584, bloody battles again erupted across the Flanaess.
In the southwest, unexpectedly, the orcs of the Pomarj rose up with a half-orc leader. They moved into the eastern sections of the Principality of Ulek and also the southern lands of the Wild Coast. Queen Yolande of Celene refused aid to the surrounding human nations, so the orcs were stopped at the Pass of Celene by dwarves, gnomes, humans and a few elves (acting independently). All were outraged and infuriated at the Queen over this, but the half-orc leader, Turrosh Mak, was happy with what he'd taken, as he knew there was no force strong enough anywhere nearby to pose a serious threat.
In the north, Ket made its move against Bissel and eventually forced a surrender. At the same time a horde of giants and humanoids moved out of the Crystalmist Mountains, right into the Grand Duchy of Geoff, Sterich, and Yeomanry. It was called the giant troubles and no single cause has been agreed upon. It is believed that Zuggtmoy, freed from the Temple of Elemental Evil established an alliance with Iuz, and along with Underdark aid from Lolth, drew the giants out. The object of it all was to give the Keoland and Furyondy alliance something else to worry about from the west while simultaneously tied up in the north with Iuz, therefore making it impossible to overrun Iuz's forces.
Belvor of Furyondy, along with elves and rangers from the Vesve Forest, did stall Iuz's drive into Furyondy, securing Chendl in the process, while Veluna held off the Kettite forces.
The utter collapse of the Great Kingdom happened at this time, with the secession of the North Province. Triggering the secession was Overking Ivid V (a decidedly mad monarch), who executed his noble Generals when his advances against Nyrond failed. After this he had them raised again as undead. Nyrond defeated Aerdy, while the remaining nobles of the Great Kingdom had Ivid assassinated. On the hells of his death, the priests of Hextor (who had been providing the initial reanimation services) appeared and raised Ivid as an undead monstrosity. Instead of simple executions he demanded wholesale massacres. Assisted by the humanoids of the Bone March the North Province quit the Great Kingdom forthwith, leaving nothing more than infantile states mostly ruled by undead minions of Ivid the Undying.
The Scarlet Brotherhood had theretofore supported the Iron League merely to have a buffer between themselves and Ivid. When the Great Kingdom fell apart, however, the Brotherhood insisted that the Iron League submit to them. When this demand was met with refusal, the Brotherhood retorted with its usual flair, and assassinations of nobles and rulers suddenly became very common. The Brotherhood took over the Azure Sea, having seized the Sea Prince's land they hungered for Gradsul, but couldn't manage a decent offensive. Not all of the Iron Leauge met with a tragic end, though - in Ironwall, Cobb Darg had always known that his support came from the Brotherhood, and as Idee and Onnwal were falling at the Scarlet hand, he had every agent of the Brotherhood executed or exiled. He also relied on the swamps of Sunndi to guard against military advances.
Finally at the close of 584 CY, the Scarlet Brotherhood (for unknown and still only vaguely understood reasons) began spreading word of peace. In Harvester of 584 CY, in the Free City of Greyhawk, which had gone untouched by the war, came the Day of the Great Signing. On that day, something happened in the Grand Hall where the peace treaty was to be signed. No one knows exactly what happened, but apparently following a magical battle through the Old City, two members of the powerful cabal known as the Circle of Eight were dead, unable to be resurrected, their clones destroyed: Otiluke and Tenser. It is said that one of their own, Rary of Ket, turned traitor for reasons unknown. Rary fled with Lord Robilar to the Bright Desert. Why this occurred is still a matter for speculation.
Despite this, The Treaty of Greyhawk was signed marking the 'official' end to the Greyhawk Wars, though border skirmishes continued on, and various nations launched counterstrikes to regain lost lands for several years beyond Harvester of 584 CY.
