What is the justification for attitudes towards armament and war?
Competition is a product of the natural world. It is a phenomenon that all self-propagating organisms deal with. It is a zero sum game ultimately, on a finite world (although maybe not??).
Direct conflict over resources can occur with a gain for one party and a loss for the other. Resources could be shared, or used more efficiently but the more common strategy seems to be conflict or fighting.
Gat would say that this is due to the success that conflict has (maybe only in the short term though). It seems that agriculture or settling might allow the other strategies to propagate. This is ‘gene-culture’ interaction that Gat refers to.
You can see the senseless arms race, tit for tat. Or you can see the constant need for suspicion based on basic evolutionary logic.