As civilizations were just getting started, the countries were just...hunting humans and other animals. However! A good portion of them noticed something; they can just stay in one place and get a steady supply of food there.
So the human-eating went down, but war raised up. Countries are territorial, so they're naturally are down for a little murder when someone dares breathes in their general direction.
Over time they kind of evolved into having a more human appearance and form. So, they assimilated themselves into human culture and society.
