The game does not support the existence of Yevon before the war between Zanarkand and Bevelle (Summoners and machina). History was simply rewritten by the victors, the summoners.
Touche! :fencing:
As I recall Bevelle won the war. I know someone states in the game that "the summoners didn't stand a chance against Bevelle's machina". As a last resort to let Zanarkand "live on", Yu Yevon created Dream Zanarkand.