The Machina War (マキナ戦争, Makina Sensō?) was an event that occurred one thousand years prior to the events of Final Fantasy X. It was a war waged between the city of Bevelle and the city of Zanarkand. It is unknown what started the war, but it ended with the creation of Sin, causing death and sorrow to rain down on Spira for the next 1,000 years.
In the war, Zanarkand relied on their summoners, while Bevelle built machina so powerful that civilians were worried they could destroy Spira. The most powerful machina was Vegnagun, but it could not be used due to its inability to tell friend from foe and hence was stored away underneath Bevelle in secret. A man from Zanarkand named Shuyin infiltrated its lair and tried to operate the machina, but was stopped by his lover, summoner Lenne, before both were gunned down by Bevelle forces.
As told in Final Fantasy X-2.5 ~Eien no Daishō~, summoners used to live on Besaid Island during the time of the Machina War, where they were trained to fight against Zanarkand while living a life of suppression regardless of their own desires. Bedore was the old name for the Al Bhed race, who were treated as the lowest class in society and worked in factories manufacturing weaponry and machines and were sometimes blamed for worsening the war. "Fake Bedore" were robotic Bedore created to help fight the war. They wore yellow suits and goggles, wielded long wire-like whips and were weak, lacking any battle prowess or agility. One day mages and assassins from Zanarkand invaded Besaid, carrying bombs that resembled blitzballs to eliminate the summoners.
Bevelle had the upper hand over Zanarkand's summoners. Knowing this, Zanarkand's leader, Yu Yevon, turned all surviving citizens of Zanarkand into fayth—with the exception of his daughter, Lady Yunalesca, and her husband, Lord Zaon—to summon a Dream Zanarkand. He created Sin as his armor to protect the dream metropolis, but as his humanity faded Sin went on a rampage and ultimately ended up destroying Zanarkand. As soon as the news of Sin reached Bevelle, a ceasefire was called and the war ended.
The effects of the war are still visible in modern Spira from the machina ruins in Besaid, the Mi'ihen Highroad, Bikanel Island, and the Calm Lands. As the war's end had brought forth Sin, Yunalesca established the faith of Yevon to quell the populace's despair and bring hope that one day Sin could be banished from Spira. As told in Final Fantasy X-2.5 ~Eien no Daishou~, the Al Bhed were blamed for the war and became social pariahs, many being executed as scapegoats for the crisis. For the next 1,000 years, the Al Bhed would live in separate communities, detested by the followers of Yevon.
Machina is the Latin word for "machine."