At least we're not the only ones?
A group of chimpanzees in Uganda has been observed to essentially "make war" on a neighbouring group, in order to capture territory for their own. Over the course of ten years, members of the Ngoro group were observed to go on "boundary patrols", remaining quiet, travelling in a single file, and generally acting like soldiers do. Over the same period, the chimpanzees attacked and killed 13 members of the neighbouring group, with the result that the Ngoro chimps were eventually able to move in and take the territory as their own.