What are the origins of war?

In my world history cl we are studying the origins of war and there are two prevailing theories; some argue that war is innate and part of being a human while others argue that war is actually the consequence of competition among early (we're talking early like very first agricultural settlers 15,000 years ago) peoples over land and women. What do you think? Is war an inevitable of the human psyche or is it something that has been created by humans?