Bridget Galton talks to the bestselling historian about his duty to understand the past, no matter how horrific, but above all to remain objective.

Antony Beevor has spent too much time mulling over the nature of evil.

His bestselling war histories have led him to trawl through disturbing testimony of atrocities that have made him weep and kept him awake at night.

Yet he sees his task to understand the mentality of the perpetrators and above all remain objective.

“The historian has a duty to objectivity, to understand the past however horrific or evil things might be and not to impose moral judgements.”

Even the most heinous acts; cannibalism, rape, genocide, should be viewed in their historical context.

“Asked how he would define Hitler or Stalin, one psychiatrist said he was fairly sure Stalin had paranoid schizophrenia and Hitler a personality disorder but can everything be explained away through DNA or childhood trauma, or was there a moment when their evil was regarded as an acceptable disposition?”

Evil, says Beevor, can be subjective. “Most of us would agree genocide and the Shoah are evil but when you start to look at individuals caught up in it, how do you explain what are the elements of evil? Is it an absolute?

“One has to understand the root cause of violence is actually fear. In a macho society you can’t show fear, you internalise it. Even in an unstable violent state, hatred is not enough. To achieve real violence against the Slav and the Jews you had to mix it with fear.”

Because of the intensity of what people have been living through, he says, “fear becomes a drug and people are attracted to violence – you see that in wars.”

Beevor’s compulsion to remain scrupulously balanced earned the wrath of the Russians who wanted books such as Stalingrad and Berlin banned for their “Nazi sympathies”.

There’s a chance his latest will evoke American anger since it deals with one of the bloodiest conflicts of WWII and the shootings of prisoners on both sides.

In the freezing winter of 1944 American troops were taken by surprise as Hitler made his last stand and the Germans counterattacked in Belgium’s Ardennes forest.

“The allies’ main mistake was that in the post D Day victory euphoria, they thought the German army was finished. Their guard was down.”

Americans and Belgian civilians were at the sharp end of battle-hardened SS divisions told to take revenge for the bombing of German cities. They brought with them the brutality of the Eastern front: tactics such as mining bodies to kill their compatriots trying to bury them.

“The savagery of the SS, the killing of civilians was pretty horrific. Furious at the Belgian resistance, they attacked as they withdrew through the Ardennes, siezing young males to work as forced labour back in Germany.”

The notorious Malmedy massacre on December 17 – the subject of a later war crimes trial – saw 84 US POWs summarily executed.

But Beevor discusses the taboo of multiple American reprisals, including a similar atrocity at Chenogne involving 80 captured German soldiers.

“It was the exasperated reaction of exhausted men. Partly a response to their anger and humiliation at being caught napping. They went a bit beserk. There has always been a killing of prisoners in wars but on the whole historians have never really written about it, especially when it comes to the actions of their own countrymen.”

Official interviews with officers directly after the battle revealed shooting German prisoners was not only sanctioned, “it was almost encouraged by the upper echelons”.

“In these contemporary accounts they talk about shooting prisoners in retribution. Soldiers knew perfectly well no action would be taken if they did.”

It is the slanted or even rose-tinted view of conflicts that Beevor hopes to redress in his books.

“In America there is this worship of the greatest generation who came through World War II. If World War I was a ‘bad war’ and the Vietnam War was morally dubious, World War II was the ‘good war’ to save democracy and the Jews, and there has been a reluctance to look at the less attractive sides of behaviour.

“But the idea that World War II was a good war is appallingly simplistic, totally fascile and inaccurate.”

You can, he says, “acknowledge the guts and courage of the Americans who hung on in Ardennes but see the different gradations instead of just black and white.”

Revisionism also makes his blood boil. Recent BBC coverage of the 70th anniversary of VJ day implied that dropping the atom bomb was tantamount to a war crime.

“If it hadn’t been for the atom bomb many millions more including Japanse would have died. Imposing modern morals and attitudes on an earlier period is historically illiterate,” he fumes.

Beevor’s books are compellingly readable as much for their 360 approach – from the arguments between generals to first person testimony of footsoldiers.

As a Sandhurst-trained ex officer who served for five years, he’s in the rare position of understanding how soldiers think.

“Military history has tended to attract outsiders. Social historians come to the subject not understanding soldiers, armies and how they work. They impose ideological judgements on the subject that to put it mildly leads to inaccuracy.”

That’s not to say you can’t write military history without a spell in the forces.

“It’s a huge advantage writing about soldiers if you have been in their place but there are women historians who have never served but are first class – Anne Applebaum, Lyn MacDonald made a huge effort to understand rather than impose their view.

“One really needs an integration of history from above and below if you are going to see the consequences of Hitler and Stalin on ordinary civilians and soliders.

“Even with those in high command, people are far more interested in the experience of the individual, human emotions, jealousy, resentments.”

His next project, The Battle of Arnhem, sees him digging into Dutch archives to give breadth and depth to what was dubbed the ‘bridge too far’.

Asked what draws him back to this particular conflict, the 68-year-old says: “Growing up in the post-war world you realised everyone’s lives had been defined by whether they had a ‘good war’.

“You became well aware that even the survivor’s lives had been completely changed by their experiences and there was a knock-on effect on their children. I have a compulsion to explore and understand that and after writing a few novels I find non-fiction is more interesting. Some of the stories are incredible, like the German farmer’s wife in 1945 who smuggled herself onto a train having fallen desperately in love with their French POW to try to get him back.

“There’s a whole novel in that. Our ability to survive and the moral choices we face in war. That’s the basic element of all human drama.”

Antony Beevor speaks at South Hampstead High School on December 1 at 7.30pm. handhlitfest.com