"All wars arise from population pressure." - - Robert Heinlein.
Copied almost in entirety for your perusal the origins of warfare explained:
"Evolutionary Psychology, Memes and the Origin of War" by H. Keith Henson.
"Evolutionary psychology and memetics are used here to propose a model of war. Population growth leads to a resource crisis. An impending resource crisis activates a behavior switch in humans allowing the build-up of memes (i.,e., learned elements of culture), which lead to synchronized attacks on neighboring tribes. Hamilton's criterion of inclusive fitness is invoked to account for the evolution of this species typical behavior. War as a species typical behavior in the environment of Evolutionary Adaptiveness (EEA) of humans is discussed, first as a response to an attack and then as an unprovoked attack. Unprovoked attacks are more common when the aggressor population anticipates 'looming privation.' The well known reduction in the ability of humans to think rationally in war situations is explained in evolutionary terms as a divergence in interest between the individual and his genes. Population growth at a higher rate than economic growth is seen as a major causal factor for wars."
Robert Heinlein of course a graduate of the Naval Academy, Annapolis. ALL WARS?
"Emotion clouds reason!" - - Michael Corleone, the Godfather.
"Why are we fighting people?" - - Mick Jagger.