This is of course just speculation. First yoshida mentions a 1000 year war. Ivalice was once governed by the Occuria, powerful entities with supernatural powers that relied heavily on Mist. Able to communicate with all living beings, including dragons, their rule was absolute. Some creatures had mystical bindings laid upon them, hinting that the creatures might have served the Occuria. At one point, the Occuria created the Espers who would become their servants and do menial tasks for them. However, the Espers, thinking themselves more powerful than their creators, revolted against them in what would be the Thousand Year War, led by the High Seraph Ultima.

As for the new race...

The Occuria managed to defeat the Espers and bind them in glyphs, then sealed them in unknown locations. Feolthanos, a member of the winged aegyl race, married a viera, starting a sub-race called the Feol Viera. Seeing this an abomination to order, the Occuria attempted to punish Feolthanos, but he fled into the sky continent of Lemurés where he sealed himself and his people. After the tragedy, the Occuria withdrew into Giruvegan, where they watched over Ivalice as their "all-seeing gods". My friend remembers Yoshida mentioning something about the sky for the xpac.

Take from this what you will.