I was thinking it was Sil'dih that was the third side of the War of the Magi. I remember hearing alot of black mage refrences in regaurds to Sil'dih, and Sil'dih was of the same period as Amdapoor and Nym as well. The three basically form the pre-cursers to the modern city staes of Limsa Lominsa (Nym's Desendents), Gridania (Amdapoor's Decendents) and Ul'dah (Which is a closer desendent to Sil'dih than the other two are to theirs as Ul'dah and Sil'dih co-existed for a while). Since the Sil'dihns were known for Black Magic, Amdapoor was Known for White Magic, and Nym was where Scholars origenated, I'd assume that they were the three sides. The Beladeans seem to be either much older or much younger than the other three. It also fits with how the 6th Umbal Era Started since the three basically wiped themselves out.