The war is a secondary feature, kind of. The story is about Vayne trying to allow humanity to control history.

To facilitate this, he conspires with Venat and starts invading countries, gradually expanding his territory and power. The Occurians give Ashe the Treaty blade so she will stop Vayne and allow history to be under their control, but Ashe destroys the Sun-cryst instead, refusing to become their pawn. Meanwhile, Vayne has gone pretty much insane and attacks Rabanastre in the Bahamut. Ashe and her companions manage to kill Vayne, destroy the ship, and create peace without becoming a pawn of the Occurians.

If that isn't epic, then I don't know what the hell is.