http://wiki.ffxiclopedia.org/wiki/Cavernous_Maws

This will give you all the information you need to ally to whichever nation you chose. You must however, complete a quest given in the link BEFORE you arrive at your destination city in the past in order to have access to Campaign/Campaign OPS/WoTG Missions. It's called a letter of recomendation. Blue for Bastok, Red for Sandy, Green for Windy. Good Luck.