Why is war so popular? All past civilisations have had wars, irrespective of their particular cultural assumptions and norms, so many people deduce that it must be an inevitable part of the human condition. It is convenient, of course, to think so because it helps to short-circuit guilt.
But there is no reason to believe that war is any different from other seemingly intractable social behaviours, such as slavery, incest, racism and so on, which it is possible to stigmatise, reduce or eliminate.
War, contrary to popular belief, is not all about displaced male aggression. If that was the case it would have died out when women got the vote - as was predicted at the time. And Britain's former prime minister Margaret Thatcher would have shown less relish in her war on the Falklands.
A progesterone cocktail concocted by the 'old brain' - the part that secured the most basic survival of our oldest ancestors - can excite aggressive behaviour, no doubt. But fierce sports, violent crime or watching a Quentin Tarantino movie is a far more gratifying indulgence of that particular lust.
It is undoubtedly triggered once in the field of battle. But it is a poor explanation for why nations go to war in the first place.
One current theory about the popularity of war proposes that we have several modes of perceiving reality and that we shift unconsciously from one to another. Hence, according to The Psychology of War author Lawrence LeShan, our day-to-day interactions with the world are guided by a basic sort of sensory reality. In this mode, we see people as neither all bad nor all good and believe that they are all motivated by more or less the same concerns. Problems are never all one person's fault.