There is a significant difference between writing the history of a subject some of whose sources are still living and breathing, and that of a subject whose sources are only documentary. In the past decade or two the First World War has undergone a transition from one to the other. A few centenarians can remember soldiers marching through the streets on the way to the front, or home in parades to mark what proved to be a hollow victory. Otherwise, the written word in memorandums, letters, diaries, despatches and memoirs forms the basis of our understanding of the period, together with extensive recordings made of old soldiers, sailors and airmen from the 1950s onwards.

That treasure trove of eyewitness accounts – what earlier generations routinely heard while sitting on the knee of their fathers and grandfathers – has enormous value: but old men forget. History is riddled with examples of memory warping reality; we know it from our own experience. Also, the old men, heroes though many of them were, saw only their own microcosm of war. The value of their experience is not to be diminished by the fact that the bigger picture, inevitably, escaped them. The contemporaneous record, if it exists, may well be superior, provided we have the judgement to see when for propagandistic reasons it has been doctored or distorted, or censored. While the last Tommies were still alive a natural deference to their experience shone through much of the writing about the period. Now no one is alive who served in the trenches or on a dreadnought, and the reliance is entirely upon documents, there can be, paradoxically, far more rigour in the analysis, as sources are tested against each other, and the unreliability of active memory ceases to intrude.

In looking at the British historiography of the First World War one starts with writing that is absolutely contemporaneous, and ends with that from this first era beyond living memory. Aside from history written as history there is also history written as literature – Sassoon, Graves, Blunden and so on. One also becomes conscious of the compartments into which the story of the war must be placed. Few historians have the range of specialisms needed, at least in the depth to which each is required, to tell the whole story, and the few who have tried usually have failed.

First, an understanding of the history of power, international relations since (at least) the Congress of Berlin and of European diplomacy is required to illuminate the catastrophe of August 1914. One also requires a knowledge of the political heritage and divisions in certain countries that played a leading role in the drama: Austria-Hungary and its tensions with Serbia before and after the annexation of Bosnia; the question of Belgian neutrality; the history of the rivalry between King Edward VII and his nephew Kaiser Wilhelm II, which helped create sufficient distrust in the kaiser of the British that it coloured his feelings towards this country after Edward had died and his far less provocative son George V succeeded to the throne; the feelings in France since the war with Prussia of 1870-71; and the growing chaos in Russia and its relations with states in eastern Europe.

Second, one needs the skills of the advanced military historian not simply to outline strategy and tactics after war breaks out, and to recount the movements of troops and the joining of battle, but also to link these with the political direction (or, sometimes, lack of it) of the chancelleries of Europe. Here the documentary evidence takes on a new importance, following the chain of events from politician to general to the man in the trench. One must understand the democratic pressures on politicians – in those countries with a reasonable semblance of democracy – to advance the interests of their country through warfare: understanding why, for instance, such a deluge of young men joined Kitchener’s army in the first three months of the war, and the cultural pressure not simply on them to do so, but on the government to make the most of their service.

Third – and this is neglected by too many historians of the war in a way it seldom is of the war against Hitler – there is the question of life away from the front. The political pressures and civilian unrest that led to the dissolution of first the Romanov, and then the Hohenzollern, the Habsburg and the Ottoman empires in 1917-18 say as much about the effect of the war and its pervasive influence in the ensuing decades as the final outcome itself. In Britain a prime minister was deposed and a coalition formed that would, in effect, kill one of its component parts in the years immediately after the war. A few Zeppelin raids did not constitute the Blitzkrieg that so disrupted the life of civilians during the Second World War, and Germany occupied relatively little foreign territory compared to its subjugation of Europe in 1940-44; but the profound effect

the war had on the lives of people away from the front is also a neglected subject.

In Britain the effect of 19,000 men dying in one day – 1 July 1916, the first day of the Somme – is beyond our computation today, when the death of a platoon of soldiers in Helmand quite rightly gains national recognition and prompts deep reflection. It is the job of the historian to try to convey that titanic sense of loss, over those first few days of July 1916, as telegrams arrived in homes all over Britain informing parents, wives and children of the fate of men who would never come back. It is as yet inadequately done, perhaps because of the stiff upper lip that pervaded the 20th century, or perhaps because of sheer inability to comprehend the scale of the disaster.

II

The historiography of the war began when the war did. On the most basic level there was a running commentary in the press. Further up the scale of debate and analysis, Oxford University Press quickly published Why We Are At War – the authors given as “Members of the Oxford University Faculty of Modern History”. The book is subtitled Great Britain’s Case, and the historians outline the background to the events of July 1914. Their account of the neutrality of Belgium and Luxembourg and the development of alliances between the main powers since 1871, and their examination of the policies of individual nations, were the leaping-off point for subsequent generations that examined the concatenation of events culminating in the declarations of war. The book went through several editions in the first few months of the conflict as governments made available correspondence and documents that presented each nation’s justification for its course of action – Britain’s Blue Book, the German White Book, the Russian Orange Book and the Belgian Grey Book.

The respective justifications told only part of the story, for to tell it all would have caused discomfort for all concerned. The necessary incompleteness and deliberate distortion at least provided scope for the historians of the next century to try to piece together every aspect of the story; which eventually, more or less, one or two did. But Why We Are At War, however time has compromised it as a source, is a valuable document for what it says about the feelings of the people in the autumn of 1914. It is unequivocal in its support for the line of the British government and the righteousness of the fight; there is none of the nuance that would come into other, later accounts.

A number of popular histories appeared in the years after the Armistice, not least Winston Churchill’s The World Crisis, published in five volumes between 1923 and 1931. For much of this time Churchill was chancellor of the Exchequer, but his political life was still overshadowed by his failure as First Lord of the Admiralty and the debacle of the Dardanelles. Churchill wrote the book because of his romantic attachment to writing the history of his own nation; because he needed the money; but above all because he felt he had to justify his conduct in 1914-15, and later in the war when he returned to front-line politics from the front line itself. The history of the First World War would ever be as much a political history as a military one.

Churchill knew what he was doing; he described the work as “not history, but a contribution to history”. More valuable, in terms of its surprising objectivity, were the two volumes of Lloyd George’s War Memoirs, written with the benefit of greater distance in the early 1930s. Of the general histories still read today the first truly rigorous one that probed more deeply was Captain Basil Liddell Hart’s. He was a veteran of the Somme; his The Real War was published in 1930 and is still in print today under the title History of the First World War. Having experienced the rigours of war (Liddell Hart was shell-shocked, gassed and wounded, and saw much of his regiment wiped out in July 1916), he strove to pursue more profound truths rather than simply retail events. One, based on his own experience, was that frontal assault achieves nothing apart from hefty casualties. So influential was this view that Liddell Hart ended up advising the government at the outbreak of the Second World War.

In the 1920s there was a slew of memoirs by soldiers and sailors, as well as by other politicians. Regimental histories, also popular at the time, tended to give accurate, but dry, accounts of military activity. Of the general histories written by those without an axe to grind, one of the more entertaining and insightful is Charles à Court Repington’s two-volume The First World War, published in 1920. In more ways than one it has all the immediacy of journalism, and not just because of the near-instant way in which it was written. Repington, an Old Etonian and a member of the Wiltshire squirearchy, had once had a glittering military career. However, while posted to Egypt in the early 1900s he’d had an affair with a government official’s wife, and had then broken the promise he had given to a senior officer to keep away from her. He was forced to resign his commission; a lieutenant colonel in 1904, he could well have been a general when war came. Instead, he was the war correspondent of the Times; and by 1914 so many of Repington’s contemporaries were senior officers that he had privileged access not just to information, but to the Western Front itself.

Repington’s two volumes are a history of the conflict told through the medium of a memoir, compiled as a journal. They are a compelling read, not least because he also had superb political contacts: indeed, when his work was published, so many of them found their private conversations had been retailed for the entertainment of the reading public that he suddenly found himself short of friends. The books are packed with instant observations of the war, both on the home front and occasionally in France, and are not academic history by any means. They see the story from one viewpoint only, which is Repington’s: but they are vivid, atmospheric, honest and dramatic. Wars are fought in cabinet rooms as well as on battlefields, and Repington’s eyewitness accounts of both make his book an essential source today. He was also the man who first used the term “the First World War”, in September 1918: not so much to coin a phrase to describe a conflict involving international empires and, since the previous year, America, but to warn that there might one day be a second one.

III

The modern school of First World War history has its origins in the 1960s, at around the time of the 50th anniversary of the conflict. It is from this time onwards that popular history – that is, books written with the intention of being read by an intelligent general public, rather than just a small circle of elevated academics – begins to evolve to its present sophisticated state, and standards of scholarship rise considerably. Put crudely, history moves from having hardly any critical apparatus to being supplemented by pages of footnotes and bibliographies. Ironically, however, the new vogue for popular history of the First World War began with a book that displays none of these qualities – Alan Clark’s The Donkeys, published in 1961.

The book is an attack on the quality of generalship, notably an assault on Sir Douglas Haig. Although praised on publication for its readability and wit, it was also roundly condemned by serious historians for its lack of rigour, and the hostility against it has increased over the years. Clark had been an apostle of Liddell Hart, whose own methods he did not follow. This is not least because Clark, who had earlier attributed the phrase from which the book takes its title – “lions led by donkeys” – to a member of the German high command, eventually confessed he had made it up. Haig’s diaries are often quoted, but selectively. The book is a clever piece of propaganda and manipulation of (usually) the truth, and its revisionism created an entirely new view of the war and how it was fought. It is, however, a view that more reputable historians have sought to correct for the past half-century.

The late Professor Richard Holmes (whose books The Little Field Marshal, on Sir John French, and Tommy, describing the life of the private soldier, are models of serious research and objective writing) accused Clark of having brought “a streak of sheer deception” into the historiography of the period. Sir Michael Howard called it “worthless” as history because of its “slovenly scholarship”. Unlike later historians, Clark did not attempt to explore whether there might be two sides to the story of apparently weak British generalship.

The BBC’s landmark documentary series of 1964, entitled The Great War, stimulated great interest in the subject, not least because of the realisation that the generation that survived it was beginning to die. The series filmed numerous veterans and prompted a vogue for oral history; the Imperial War Museum undertook an enormous, and hugely valuable, project. For the rest of that generation’s life oral history was given more emphasis than documentary records, the focus on it becoming more intense as the numbers with first-hand recollection of the events declined. The half-centenary also prompted a further wave of books. In America, Barbara Tuchman’s The Guns of August had appeared in 1962. George Malcolm Thomson covered similar ground in his highly acclaimed The Twelve Days, published in 1964, a detailed account of the diplomatic activity between 24 July and 4 August 1914.

But the 1960s also brought the beginning of a far bolder interpretation of the war and its causes. A J P Taylor, the highest-profile historian of the time, published in 1969 War by Timetable, which argued that the mobilisation timetables of all the great powers – whose generals had prided themselves on being able to mobilise faster than their potential enemies – led to an inevitable drift towards a war no one actually wanted. This notion that the First World War was not a deliberate plot by Germany to expand its power was highly controversial, and led to the birth of the two rival schools of thought that have dominated the study of the war in recent years: one that says Germany was hell-bent on world domination, the other that says the war happened by accident.

Three years later the first volume of Correlli Barnett’s Pride and Fall tetralogy, The Collapse of British Power, although only in passing about the First World War, contained some telling insights about it – such as how many of the men who fought the war had, for the first time in their lives, proper food, clothes, boots and their own bed to sleep in.

In 1998 two serious British historians of different generations published authoritative histories of the conflict. Sir John Keegan’s The First World War was based almost entirely on secondary sources, but written with a measured expertise that made it the perfect entry-level guide to the fighting, taking into account almost all of the scholarship since 1914. Professor Niall Ferguson’s The Pity of War was a different beast; a more political book, making greater use of primary sources, and offering a more controversial judgement: that the kaiser had not wanted war, and Britain’s security did not rely on Germany’s defeat.

The next great landmark of British war studies – and in one respect the most frustrating – was the first volume of Sir Hew Strachan’s The First World War, published in 2001. It is frustrating because this titanic volume (it is nearly 1,200 pages long and covers all theatres of the conflict) takes the story in Europe little beyond the opening phase of the war. But it concentrates on more than just the military angle, looking at the supply of munitions, the colonial questions and the means of financing the conflict. Sir Hew promises two more volumes, neither of which, sadly, is yet in sight. When finished, they will be what the war has always needed – a definitive, comprehensive and international history based on exhaustive and rigorous scholarship. For now, the centenary of the conflict approaches and the war still awaits the complete history it deserves.

IV

The anniversary has prompted not just more publications, but also a renewed argument about the necessity of fighting such a horrendous conflict. To generate publicity for their recently published populist works, Sir Max Hastings and Jeremy Paxman between them reopened the argument over whether the war had been necessary: and Sir Max and Ferguson had a two-part television battle about it, an unfair fight, given that Ferguson is a serious scholar who fits his conclusions to the evidence.

In a magisterial review in the Times Literary Supplement last autumn of Sir Max’s and two other books – Professor Margaret MacMillan’s bizarrely titled but widely acclaimed The War That Ended Peace and Brigadier Allan Mallinson’s 1914: Fight the Good Fight – William Philpott, professor of the history of warfare in the world-renowned war studies department at King’s College London, drew some distinctions between rigorous and populist history, and pointed to how high the standards now are, not least following Sir Hew’s entry into the field. Philpott assessed the value that

MacMillan, as a scholar of international diplomacy, brings to the complex series of events that caused the war, and praised Mallinson’s dissection of military questions with his “trained soldierly eye”. Sir Max’s work, by contrast, Philpott dismissed as “broad-brush and judgemental”, something for which, a century after the events, there is no need if only a writer will look carefully at the wealth of documentary evidence available to him, and assess it free from received wisdom.

In taking our history more seriously, and demanding from historians evidence that prevents the presentation of fact from being recast as simple assertion, we have moved on from the Arthur Bryant school that still sets the model for populist history. The trouble with broad-brush is that it misses detail and the other side of a question, and sometimes commits worse sins – Philpott said Sir Max’s confident descriptions of battle came “often at the expense of explaining it clearly and accurately”, perhaps because of the author’s reliance on what the professor waspishly, but with an appropriate choice of metaphor, called “his own army of research assistants”. He condemned Sir Max for taking little notice of the detailed scholarship on the subject that has transformed and deepened perceptions of the war in the past 50 years. And he hinted at a weakness of basing judgements on accounts of those who were there: they did not see the bigger picture.

Of all the recent works of history, one stands far above all others, and should be regarded as an indispensable read for anyone who wishes to understand why the war happened: Christopher Clark’s Sleepwalkers, published in 2012. Professor Clark is a German specialist, but also steeped in the international politics of the period before the Great War. He recently, and memorably, dismissed Sir Max by saying that “he is not a historian. He is a man who writes about the past” – a suitable essay subject for a degree examination if ever there was one.

Although he covers much of the same ground as MacMillan, whose scholarship is hardly meagre, Clark appears to have looked far more deeply and widely in archives than she has. Without an army of research assistants, but relying on a grasp of the main languages involved and a serious study of foreign archives, Clark gets to the heart of the two principal questions: why Gavrilo Princip felt moved to shoot Franz Ferdinand and his wife when they went to Sarajevo on 28 June 1914, and why the ensuing quarrel could not be contained to one between Austria-Hungary and Serbia. After much inquiry, presentation of evidence and discussion, he reaches a judgement: that the kaiser didn’t want war, and that a war occurred was largely down to the bellicosity, incompetence and weaknesses of others.

As the historiography of the Great War enters its second century I suspect that Clark’s view will gain more adherents, not least as a more nuanced and thoughtful understanding of this abominable conflict becomes more possible now that those who remember it are dead. We might even finally discover that the Germany of 1914 was nothing like the wicked and evil Nazi state we had to fight in 1939, and, unlike that later conflict, that nothing about the motivations behind it was simply black or white.

Simon Heffer writes for the Daily Mail. His latest book is “High Minds: the Victorians and the Birth of Modern Britain” (Random House, £30)