But other conflicts span regions and can stretch on for decades. Over the centuries, humans have described war as everything from a glorious struggle to a pointless, violent and inhuman activity. Have we always made war upon one another?

To answer the question, we first must define war. According to the Merriam-Webster dictionary, war is the "state of usually open and declared armed hostile conflict between states or nations." That definition helps us narrow down when humans invented war. If we're talking about states or nations, we must focus on early civilizations. Before civilization, all humans were tribal and at least somewhat nomadic. It was only after we developed agriculture and settled down that we could build the resources needed for war.