During the war, lovers Lenne and Shuyin were drafted into the Zanarkand armies. Shuyin, fearing for Lenne's survival, infiltrated Bevelle and attempted to activate the machina, Vegnagun, in order to put an end to the war by decimating Bevelle. However, Lenne set out after him. She managed to stop him from wielding Vegnagun, but was followed by Bevelle Soldiers, who proceeded to shoot down both Lenne and Shuyin.
Near the end of the war Bevelle's machina gave them the upper hand and Zanarkand was about to lose, when the survivors gathered in Zanarkand under the guidance of Yu Yevon. Believed to be the most powerful summoner alive, Yu Yevon directed all Zanarkand citizens to flee to the nearby Mt. Gagazet. There, refusing to admit the fall of their beloved city, the people of Zanarkand let themselves be turned into Fayth, all gathering on a massive wall on Gagazet's slopes. Yu Yevon used them to begin the summon of a city; a new, ideal Zanarkand, forever at peace and eternally holding alive the memory of its former glory.
In order to protect himself while summoning the city, Yu Yevon gathered millions of stray pyreflies around himself, forming an armor which would later became known as Sin.
In order not to become distracted from his summoning, Yevon "programmed" a series of guiding instincts into Sin: among them, to attack any larger human settlement, to attack any machina, and to respond to aggression with overwhelming force. Unfortunately Yu Yevon lost control of Sin and became trapped inside its instinctive behavior, from then on living only to cast the summoned city.
No longer under control Sin attacked the nearest human settlement, completely destroying the real Zanarkand, and proceeded to decimate the incoming Bevellian army. From that point onwards, Sin destroyed any large city, quickly becoming a terror to all Spirans and uniting Spira under a common fear.
On the eve of Zanarkand's destruction, Yunalesca, herself a very skilled summoner, managed to escape the doomed city with her husband, Zaon.
Eventually Yunalesca and her husband traveled back to Zanarkand's remains where she turned Zaon into a particularly powerful Fayth, dubbed a Final Aeon, and defeated Sin for the first time. However, at the moment Sin's shell was cracked, Yu Yevon took control of Zaon's Aeon, forcefully severing the mental link between Zaon and Yunalesca, killing her.
With Sin's "defeat", a short period of peace settled on Spira, known as The First Calm. Unfortunately, within a couple of months, Yu Yevon was able to regenerate a new Sin using Zaon's Aeon as a core, and Spira's plight began anew.
Bound by her promises towards both her father and Bevelle, Yunalesca remained in Zanarkand as an unsent. It is assumed that she crafted a deal with Bevelle: in exchange for all people honoring the memory of her father, Yu Yevon, she would ensure an immunity to the city against Sin's rampage, and personally show anyone who comes to her a way to defeat Sin.
During the following decades, Bevelle's leadership slowly changes into a religious organization whose central figure is "Yevon", a benevolent teacher who tells Spirans ways to atone for their faults and reliance on machina, which supposedly had brought Sin to their world.
While Yevon slowly establishes its hold over most of Spira, summoners from all around gather and try to vanquish Sin, with little success. Finally, a summoner named Gandof is able to defeat Sin, tearing the Calm Lands asunder and isolating the Remiem Temple in the process, thus creating The Second Calm. However, Gandof suffers the same fate as Yunalesca and dies. As before, this calm is short-lived and Yu Yevon soon rebuilds Sin which starts its rampage again less than a year later.
After his death, Gandof was named "High Summoner", a title which would from then on be bestowed posthumously on all who had defeated Sin. Statues of Gandof were built and put in all of Spira's temples and his story is told to all Spirans as an example of honor and sacrifice to be followed. To defeat Sin, High Summoner candidates, known only as "Summoners", would journey through a series of Yevon temples, gathering powerful Aeons at each temple in preparation for obtaining the Final Aeon in Zanarkand and combating Sin.
Seymour and his mother are exiled to the island of Baaj.
Sometime in the next seven years Seymour and his mother embark to Zanarkand to defeat Sin, however when his mother sacrifices herself to become his Final Aeon as Anima, Seymour is horrified and breaks off the pilgrimage.
Jecht appears in Spira, having been sent from the Dream Zanarkand.
Braska embarks on a pilgrimage to Zanarkand for his daughter's future and the memory of his wife, and brings about yet another Calm with the aid of Jecht and Auron. Braska dies from the final summoning.
Attempting to rebel, Auron is killed by Yunalesca but before he dies he passes his duties towards Yuna on to Kimahri Ronso.
Shinra receives enormous financial support from Rin, and begins trying to use Vegnagun to siphon energy from the Farplane. But, he is unable to complete the system for utilizing this energy in his generation.