The is story releated! Throughout the game you will constantly be running to Ranvi back in ravensthrope and asking to view the alliance map. Here you will see all the location that you are expected to liberate based on your player skill level as well as what locations you have already finished. Eventually you will see Cent as an option. Simply select it as your next target to ally then complete the story releated missions in Cent to recieve the achiement. I found most locations took me 30-60 minutes to complete. If the skill level of the location is red, it means you are under leveled and the game will recommend leveling up first. I would also recommend this how ever there is an achievement for killing X amount of people that are higher levels than you.