A handout picture released by the Syrian opposition's Shaam News Network shows the mass burial of those killed in Houla. Photograph: AFP/Getty Images
In his account of his time covering the war in Vietnam for Esquire, Dispatches author Michael Herr explains how he once asked a US helicopter door-gunner how he could shoot women and children. The man answered: "It's easy. You just don't lead them so much." It was a flippant and chilling answer to a question that occurs in every conflict – how, and why, do fighters commit those atrocities?
In the aftermath of the massacre in the Syrian village of Taldou, near Houla, in Syria – where it seems in all likelihood that Shia Alawiteshabiha gunmen loyal to the regime of President Bashar al-Assadmurdered scores of Sunni civilians – it is a question that is inevitably being asked again. Having covered more than a dozen wars in which I have tried to understand the mechanisms of violence, I have come to realise a terrible reality: Herr's door-gunner, in his callous reply, was right.
Because we are so shocked when confronted by atrocity and war crimes, especially involving women and children, we tend to invest them with a sense of moral – or immoral – drama and purpose often absent from the act.
That is not to say that we should not find these killings abhorrent, or demand that those responsible be brought to justice. But in these circumstances people kill because they can; because they believe they can act with impunity; because they have been asked to and rationalised the utility of the act; and because they have persuaded themselves that their victims' humanity is of lesser value than their own.
What I am talking about is something more commonplace than Hannah Arendt's notion of the "banality of evil"; something summed up for me in a remarkable picture taken by my friend Ron Haviv when he photographed the Serb militia of "Arkan" Ražnatovic and his men-murdering civilians. In that picture, one of Arkan's "Tigers" is seen "dead checking" a Bosnian Muslim woman they have shot by kicking her, a cigarette held insouciantly aloft. Not banal, but casual.
That is the real question: how is it that killing civilians can come to be normal for those who are doing it.
In Rwanda during the Hutu interahamwe killing, as Philip Gourevitch, author of We Wish to Inform You That Tomorrow We Will Be Killed With Our Families, documented, gangs had been primed by hate radio with the notion that their victims were "cockroaches". It is a mistake, however, to believe that people can be persuaded to commit crimes against humanity by a short-term exposure to the rhetoric of hate. In massacres with a sectarian component, – which appear, at first sight at least, to have been a component in what occurred in Taldou, regardless of what orders were given by officials of the regime – the process of dehumanisation is likely to have been the slow work of a lifetime.
Paul Connolly, a Northern Irish academic, established in a piece of seminal research on sectarian attitudes conducted at the end of the Troubles that such a process begins very young indeed, formed by family, community and culture. He discovered that by the age of three, children from Catholic communities were already twice as likely to be hostile to a police force regarded as pro-British as Protestant children; by six, a third of children strongly identified with their community, while a significant minority were already making sectarian statements.
Similar research, conducted by Daniel Bar-Tal at Tel Aviv University, asked Israeli children to explain what "Arab" meant to them, identifying similar negative connotations becoming established in early years by the same social mechanisms. In peacetime, these tensions between groups are manageable, to a degree. But when conflict comes, it imposes its own explicit values – a "conflict culture" that values in-group cohesion and out-group hostility, which not only plays on these existing tensions, (from negative stereotyping to the dehumanisation of the other), but actually ascribes to them a positive value.
In these kind of conflicts, those who display the fiercest loyalty to their own group and fiercest hatred of the "other" have a special usefulness – providing not only the most ruthless killers because they are challenged the least by the morality of what they are doing, but often also acting as examples of what the new culture of conflict "requires" of all members of the group.
For in the end, this is what war does – and not only in authoritarian regimes like that of Assad. The same processes occur whenever men are asked to kill others. It is why each generation throws up its horrors, and why we should not be surprised even as we are horrified by each new My Lai, each new Sabra and Shatila, or each new Srebrenica.