Machina War

The Machina War was an event occurred one-thousand years prior to the events of Final Fantasy X. It was a war raged between the city of Bevelle and the city of Zanarkand. It is unknown what caused the war to start, but what is known is that the war ended with the creation of Sin which caused death and sorrow for the next 1000 years.

In the war, Zanarkand relied on their Summoners while Bevelle built Machina so powerful, that civilians worried that they could destroy Spira. One machina of note was Vegnagun, which could not be used due to its shear power and was stored away underneath Bevelle in secret.

In the end, it was obvious that Bevelle's might would win the war very easily and that Zanarkand's summoners would not stand any chance of fighting them. Knowing this, Zanarkand's leader Yu Yevon turned all surviving citizens of Zanarkand into Fayth in order to summon a Dream Zanarkand. He then created Sin, which ultimately destroyed Zanarkand.

As soon as the news of Sin reached Bevelle, a ceasefire was instantly called and the war ended.