Journalism is said to be the first draft of history, but it is often disappointing to find that the second or third drafts, by historians, move little further in establishing the truth about what happened. Errors made by reporters in the heat of the moment, instead of being eliminated, have become part of the authorised version. Factors that are crucial in creating the context within which events occurred go unmentioned.

That context is the mix of hopes, fears, hatreds and habits, frequently the fruit of an individual's or a community's previous history, which are so important in determining how they will act. This is particularly true of wars when, even a few seconds after being truly frightened, it is so difficult to evoke in one's mind what those moments of terror felt like. "Can a man who is warm understand a man who is freezing?" Alexander Solzhenitsyn famously asks in One Day in the Life of Ivan Denisovich.

The experience of mass fear, when large groups of people believe they are in danger of extermination or enslavement, is so important in shaping the historical instincts of countries and governments. Most European countries have suffered devastating war, foreign occupation or both over the past century, with exceptions being the British who remained unmarked by any recent experience of being wholly at the mercy of another's armies.

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For all the current focus on 1914 and the mass slaughter on the Western Front, the British experience of the First World War was, in many respects, not as bad as what is happening to the Syrians today. Britons were not driven from their homes and their whole families were not threatened, whatever death toll from the trenches. Most people are more frightened for their children than themselves, which is why the Syrian, Iraqi and Lebanese wars created such all-embracing terror.

It is not that the British have never had such an experience of total war. But to find it you have to go back more than a thousand years, to the long period when the Vikings had taken over much of the British Isles and were ravaging the rest. They are the subject of an exhibition at the British Museum called Vikings: Life and Legend, which is more revealing in many ways about British attitudes to violence and war than are any current reflections about the First World War. Reading academic commentary on the Vikings and listening to the talk of people viewing the exhibits, there seems to be a common disbelief about how nasty wars can be and a common desire to find alternative explanations or excuses for the perpetrators of war crimes.

In the case of the Vikings, many historians since the Sixties have ignored compelling evidence that they were mass murderers, whose atrocities were the equivalent of those carried out by SS divisions invading Poland 75 years ago. Writers all over Europe at the time of the Vikings, whose very name in Old Norse means "pirate", are at one in describing their savagery. But their terrified accounts of what happened were set aside by experts as biased because the eyewitnesses were often monks whose monasteries were prime targets of the raiders. Emphasis was instead put on the role of the Vikings as traders (though their main trade was in slaves), sailors, poets (though the Sagas were written much later) and craftsmen (though the most impressive objects in Viking hoards were looted from other countries).

The centre-piece of the present exhibition is the remains of what is known as Roskilde 6, an 11th-century ship, discovered and excavated from the bottom of a Viking port in Denmark in 1996-97. Skilled though the Scandinavians may have been at building better warships than anybody else, it is also worth recalling that these vessels played the same role in attacking other peoples in Europe as German tanks did much later.

It is extraordinary that the myth of the Vikings as misunderstood spreaders of Nordic culture should ever have had any credibility. My late friend Patrick Wormald, one of the great experts on Anglo-Saxon England, writing in The Anglo-Saxons, edited by James Campbell, mockingly derides the idea that the Viking attacks were "mere plunder raids which were insufficiently sensitive to local religious susceptibilities".

Signs are overwhelming that the Vikings waged total war against the Anglo-Saxons from the time of their first recorded raid in 789. These escalated by 865 into invasions by hundreds of ships bent on conquest and settlement. Wormald notes that the kings of East Anglia and Northumbria were defeated and then seemingly killed in a sickeningly gruesome Viking ritual known as "the blood-eagle", which involved "ripping a victim's lungs out of his rib-cage, and draping them across his shoulders like eagles' wings".

The pro-Viking lobby claim this is exaggerated stuff and there is no proof of such Viking atrocities. But the absence of evidence is scarcely surprising. The invaders, themselves illiterate, were so destructive that almost no writings survive from the conquered Anglo-Saxon kingdoms.

The Anglo-Saxons fought back heroically, reconquering much of the country, only to succumb to a final Viking onslaught in the early 11th century. The warfare never lost its ferocity: if I look out the front door of the house where I am writing this in Canterbury, I can see the city's great medieval walls behind an earlier version behind which local people withstood a three-week siege by the Vikings from 8-29 September 1011. The Vikings finally stormed and sacked the city, taking prisoner Archbishop Alphege whom they held hostage. Angered by his refusal to allow the people in Canterbury to pay a ransom for him on the grounds that they were already too poor, the Vikings beat him to death at a drunken feast.

The intensity of the violence was equal to anything in present-day Syria. Not many people have heard of the St Brice's Day massacre on 13 November 1002 when the Anglo-Saxon king, Ethelred the Unready, ordered the deaths of all Danes in his kingdom. In Oxford, surviving Danes barricaded themselves in a church (where Christ Church Cathedral now stands) and successfully defended themselves until townspeople set fire to the church. The skeletons of some 34 young men believed to have been killed in the same massacre were discovered under St John's College in 2008.

Overall, the Scandinavians have a lot to apologise for. The leader of almost every Viking raiding party or army about which anything is known committed crimes which today would see them charged before the International Criminal Court.

The exhibition at the British Museum does not quite make up its mind about the Vikings, though it is scornful of the view that their expansion was "essentially a violent one". At the same time, the authors of the book about the exhibition cautiously admit that the stereotype of bloodthirsty killers cannot be entirely discarded. Finally, they make the excuse that: "Viking warriors made up only a small and not particularly representative proportion of Scandinavian society as a whole." Of course, the same could be said of the relationship between the SS and German society in its entirety.