Eorzea was first inhabited by gods and goddesses, which the wandering tribes that settled the land started calling the Twelve. The gods blessed the tribes that came to the savage land with welfare, but the tribes began fighting with each other, and war tore Eorzea apart.
Could this 12 be referring to the Lucavi or the Zodiac? I know this has been exclusive to Ivalice only, but I wouldn't mind seeing it always liked them. Also in addition to this if zodiac does play some sort of role which has never been announced, I liked in Tactics how you were able to put in your DOB and I believe there were benefits depending on your sign. Nothing game breaking just small stat differences or something, I like the idea of stats being based off zodiac sign rather than race personally.