My thesis is that humans are a violent species, and that they enjoy killing each other. A lot of people say I am wrong. Not much else, just that I am wrong.
War seems like a good way to solve a problem, even fun and exciting to watch, until it's your ass (or your son or daughter's) they call up to go. Easy to go to war when you sit at a desk and people you've never locked eyes with go off to kill and die.
Most people aren't violent and would get physically sick if they had to kill someone (though the primitive bloodlust instinct remains in us all). I think the problem is a lack of empathy and personal consequence for those in a position to send soldiers off to die to "fix" their problems. Drones make it even easier, these days.