Updated 03-06-2016 08:09 PM
This achievement is unlocked by clearing out all the safe houses of enemies and claiming them for yourself in the south. Once claimed you will be able to use the safe house as a save point, a supply refill spot, and a place to stash weapons. There are a total of 27 safe houses in the Southern territory. You can use the link below to locate all the safe houses:
Take note that there are three safe houses in the southeastern zone of the south (in the Heart of Darkness area) that are not needed to unlock this achievement as they are already claimed as yours.