At 8 am on 28 October, Edith Harms, the wife of painter Egon Schiele, died in Vienna of influenza. She was six months pregnant. Schiele had drawn Edith twice the night before in what were to be his last works. He succumbed to the same disease at 1 am on 31 October 1918. He was 28. The link between eroticism and death, latent in so many of Schiele’s pictures, seemed to have come full circle. So too did the life of the Habsburg empire, of which they were both citizens and in whose capital they lived. Five days after Schiele’s death Austria accepted defeat in the First World War, signing an armistice with the allies in Italy; its partner in the dual monarchy, Hungary, did so in Belgrade on 13 November. By then Austria was a republic, although the former emperor, Karl, refused to abdicate as king of Hungary. Like the Schieles, Karl and his young family also fell sick; they, however, all survived.

The Habsburg empire dissolved in a cycle of revolution and civil war, as did the empires of the Romanovs, the Hohenzollerns and the Ottomans. From the Baltic to the Balkans, and from central Europe to central Asia, their peoples sought to redefine multi-national conglomerates as nation states. They did so on the basis of identity, determined by ethnicity, faith, ideology or language, while peacemakers in Paris thought geographically, drawing lines on maps which were overtaken by events on the ground. Nor were the ostensible victors in the First World War in significantly stronger positions. Most faced unemployment, inflation and debt, and they too went in fear of revolution. Britain was under particular pressure, facing conflict across ‘the southern arc of empire’, from Ireland to India. The First World War did not end in November 1918, but had begun to unravel a year before, with the Bolshevik seizure of power in Russia in November 1917, and its last peace treaty, that created the new republic of Turkey, was not signed until July 1923, in Lausanne.

These major political events which shaped so much of twentieth-century history were accompanied by a steady drumbeat of death, caused not just by violence (although there was plenty of that) but also by disease. The principal cause of morbidity was the influenza pandemic of 1918 and 1919, but it was not the only major killer. Tuberculosis, malaria and hunger also played their parts. And yet neither commentators at the time, nor historians since, have shown much inclination to consider the interconnections in this ‘perfect storm’. Did sickness promote or retard revolution? Did it help end the war sooner than the allied powers expected? Did it play a part in the botching of the peace settlements? Did it contribute to the collapse of state authority and so facilitate civil war? Few have even asked the questions, and yet fewer have provided answers. Two recent major studies of the attempts to re-establish order after the Great War, The unfinished peace after World War I by Patrick Cohrs (2006) and The deluge: the Great War and the remaking of global order by Adam Tooze (2014), have index entries for inflation, but not for influenza.

The influenza pandemic hit in three waves. The first, in the spring of 1918, caused comparatively few fatalities, and given the incidence of deaths from influenza in 1917 might not have aroused particular alarm. The second, which killed the Schieles, began in August and peaked in October and November. It was responsible for 90 percent of the recorded deaths. The third was less virulent but ran on for most of the first half of 1919. By the time the Second World War broke out it was realised that the initial calculation of total deaths worldwide, 21 million, had failed to take sufficient account of countries for which statistics were less readily available. By 1942 40 million was being cited, and by the turn of the millennium estimates based on the number of excess deaths ranged higher, some even suggesting a total of 100 million, or 5 percent of the world’s population.

Such losses to natural causes made the impact of the First World War itself no more than a demographic blip. The total number of war-related military deaths has been variously estimated at between 8 and 10 million, with a consensus hovering at around 9.5 million. Although the variation and its attendant uncertainties are much less than those for the deaths from influenza, in some ways they are more remarkable. Armed forces are state institutions, and their members are paid and sometimes pensionable; in the First World War many countries made allowances to their families.  In other words, military losses were more amenable to statistical analysis. Some of the variation is due to different methods of counting. The cut-off date for deaths in the forces of the British empire was 1921, to allow for losses in the ‘wars after the war’, in the allied armies of occupation, and from lingering medical conditions incurred between 1914 and 1918 which resulted in death between 1919 and 1921. By the same token, however, those who died after 1921 from war-related injuries were not included. For example, gas warfare – for all its horrendous implications – actually killed few soldiers in the years up to 1918 but inflicted slow deaths on veterans crippled by lung conditions in the 1930s.

Undoubtedly, a calculation of the deaths caused by the First World War which counts only those in uniform grossly underestimates its effects. Some civilians met violent ends caused by enemy action: the French and Belgians killed by the advancing German armies in 1914 (about 6,500); the Serbs similarly killed by the Austro-Hungarian army and the East Prussians by the Russians, also in the opening weeks of the war; and the British killed by the German cruisers in the bombardment of east coast ports in December 1914 and thereafter in air raids (possibly as many as 1500). After the war, Germany would claim that one million German civilians were starved to death by the allied blockade: this figure was accepted by the British official historian of economic warfare, although today most historians would cut it by at least half. The total number of Armenians killed by the Ottomans remains disputed, but a conservative estimate is one million. We do not know how many Russians died in the ‘great retreat’ of 1915, when about three million fled European Russia in the face of the advancing German and Austro-Hungarian armies, or how many porters expired carrying the munitions and supplies needed for the troops of the colonial powers on the long-lines of communication in the campaigns of sub-Saharan Africa.

The number of deaths attributed to the Second World War has been creeping steadily upward from about 55 million to as high as 70 million. One of the principal causes of this progression has been the inclusion of civilian losses, and the enormous variation in the final total is an indicator of our lack of certainty as to how to count them. We routinely exclude civilian losses from the First World War total, but if we do include them we become vague and uncertain. When in 2012 the British prime minister, David Cameron, announced his government’s programme to commemorate the centenary of the First World he said the total number of war-related deaths was 16 million. In the same year, Christopher Clark in The Sleepwalkers put it at 20 million. These are simply guesses, almost devoid of scientific precision, but they remain much lower than those cited between the wars by scholars keen to warn the world of the cataclysmic effects of modern conflict. In 1920 E.L. Bogart said that ‘the loss of civilian life due directly to war equals, if indeed it does not exceed, that suffered by the armies in the field’. On that basis Hoffman Nickerson, in Can we limit war?, published in 1933, put the civilian dead of the Great War at 13 million. In 1942 Quincy Wright, professor of international law at Chicago, in a weighty, interdisciplinary two-volume study of war, put the total deaths in 1914-18 from military action and war-distributed disease at over 40 million.

There is quite a lot of double counting going on here. One cause is nationality. Were Americans who died before 1917 in the service of France or Britain counted by both the United States and France or Britain? How about Danes who fought for Germany? Another, statistically more significant, cause is disease, and particularly the influenza epidemic. Because Bogart, Nickerson and Wright could not readily differentiate disease attributable to the war from other disease, they were inclined to include it as a cost of war. If we follow that argument to its conclusion, we might arrive today at a total death rate for the First World War not of 40 million (ie roughly 10 million military deaths, 10 million civilian and 20 million from influenza), but of 120 million (the combination of the current maxima of those three categories). Numbers this big comfortably exceed the highest total for the Second World War and dwarf our capacity for comprehension or empathy. They would also be wrong: each of the military and civilian totals already includes deaths from influenza.

The points are easier to grasp when put in individual terms. Because Schiele was a great artist cut down in his prime, we think of his death in terms of the loss to culture, not to the Habsburg empire. But theoretically he was still a soldier when he died. Although twice exempted on physical grounds from military service in 1914, he was eventually called up in May 1915. As with other artists (the poet Rilke comes to mind), the Austro-Hungarian army managed to find Schiele a berth which did not expose too brutally his almost total unsuitability for a martial career. In 1916 he was put in charge of food supplies at a prisoner of war camp for Russian officers in lower Austria and in 1917 he returned to Vienna to work for the army’s administration in ways which left him free to paint and to plan exhibitions of his own and others’ work.

Schiele was not exposed to danger on the battlefield and did not die as a result of enemy action. Nonetheless, if he had been a soldier of the British, not the Austro-Hungarian, empire, he would today be numbered among the war dead by the Commonwealth (originally Imperial) War Graves Commission. It commemorates the almost one million military dead of the war from across the British empire, whatever the reasons for their demise. Edith Schiele, although she died from the same illness in the same place three days before her husband, would not be so remembered. The Commission cares for the graves of thousands of service personnel, who died not in battle but of disease, some of which may have been war related, some not. Disease, not fighting, was the big killer in war before 1914, and it still was on fronts outside France and Belgium. Ottoman military deaths from sickness were nearly double those in combat.

In recent years the Commission’s criteria for inclusion have been softened, rather than tightened, indirectly adding to the total numbers of British military dead. Private Alexander Ponton of 1^st/4^th King’s Own Scottish Borderers went with his battalion to Gallipoli in 1915 but was discharged on grounds of ill health and died of tuberculosis in October 1916. He was buried in an unmarked pauper’s grave in his local churchyard at Hobkirk, near Hawick. In 2017 the Commission commemorated him as a casualty of the war, although there is no evidence that his tuberculosis was a consequence of his military service as opposed to the rural poverty in which he was raised. Ponton was a civilian at the time of his death, but the Commission does not commemorate the civilians who were killed in either war by direct enemy action.

These variations in totals and their categorisation compound the challenge of assessing the impact of the influenza pandemic on the world’s emergence from the Great War in 1918-19. After all, the disease did not discriminate between belligerent states and neutrals. Moreover, it did not operate in isolation but in conjunction with other factors which increased its effects. In all the belligerent countries, housing conditions worsened as workers responded to the labour demands of war-related industries by migrating to the towns, while national mobilisation drew labour from the building industries. Rents rose, overcrowding increased, and tuberculosis flourished.

In 1916 the harvest failed across Europe, contributing to the outbreak of revolution in Russia the following March and prompting strikes elsewhere. The globalised food distribution system, on which Britain and Germany particularly depended, collapsed on the outbreak of war, and the consequences for continental Europe were compounded by the allied blockade of the Central Powers. In April 1917 the world’s principal neutral, the United States, entered the war and the blockade was tightened with a ferocity that embraced the neutral states bordering Germany and its allies, as well as the Central Powers themselves. On British insistence the blockade continued after November 1918 until the defeated countries signed the peace treaties, which formally ended the war. The second wave of the influenza pandemic hit peoples whose resistance to disease was already severely compromised.

On 3 October 1918 Germany approached Woodrow Wilson, the American president, to request an armistice. The allies were surprised; they had not expected the war to end until after June 1919, the date by which the American Expeditionary Force in France would reach four million men. Over the following month powerful voices on both sides, including John J. Pershing for the Americans and Erich Ludendorff for the Germans, called in vain for the war’s continuation. By then, although never mentioned by the generals, influenza was a material factor in the armies’ fitness to fight.

In the United States, the second wave of the pandemic had prompted the War Department to cut loading on the troopships by 10 percent. It could not afford the time to quarantine the soldiers for three weeks before embarkation, and was ready to bear the cost – nearly 1,000 deaths at sea for 130,000 troops delivered to France. The allied commander on the Macedonian front, where the initial allied breakthrough occurred in September, talked about advancing to Vienna and thence to Berlin, so ending the war. But influenza took two entire French divisions out of his order of battle. Between 1 October and 11 November 1918 the French on this front suffered only 264 battle casualties but on 16 October alone had 24,443 from a force of 190,000 hospitalised by disease. The Germans could not reinforce the Macedonian front because they had too few men to do that and hold firm in the west. Their offensives in the first half of 1918 had cost them about 900,000 casualties, while extending the length of front they had to hold. Over the course of July 685,000 German soldiers fell sick, nearly 400,000 of them with influenza.

Douglas Haig, the British commander, argued strongly that the war should be ended while the German offer was on the table. He foresaw the allied advance slowing as the weather worsened and the days shortened, but he must also have been aware of the threat which influenza presented to allied effectiveness. By the war’s end nearly 800,000 American soldiers had contracted it and possibly 44,000 had died. The war-winning offensive of 1919 was in jeopardy.

By the time the peacemakers convened in Paris in January 1919, they were men in a hurry and so had insufficient time for the protracted negotiations which the circumstances required. As heads of government they could not afford to be absent from the capitals for too long. Influenza was another pressure to get things done. Its lethality had abated, but, as an American, Hugh Gibson, observed on 25 February, ‘everybody has the flu or has just had it or is just going to have it’. Woodrow Wilson himself fell ill in April and seemed shaky thereafter; his disabling stroke followed less than six months later.

Another pressure was widespread hunger. Gibson worked for Herbert Hoover, the food administrator in the United States, who organised famine relief during the war and in its aftermath. Hoover warned that 400 million people faced starvation in enemy countries and elsewhere. The Americans strongly opposed Britain’s continuation of the blockade, echoing German complaints that it specifically hit non-combatants. Although Hoover’s concerns were humanitarian, those Britons who sided with him were more worried that the Bolsheviks, not the Boche, were now the enemy. They feared that hunger would stoke revolution, which would sweep from Russia across eastern and central Europe, undermining not just Germany and Austria but even Britain and France.

Death in 1918-19 came in many forms. Differentiating between whether people were killed or died for other reasons made little sense after four years of protracted and intense conflict – conflict, moreover, which had not finished. Possibly four million more met violent ends in the fighting that continued until 1923. By the autumn of 1918, war had become institutionalised in the lives of the belligerent nations. It was a part of everyday life, even if one which overturned the normal rhythms of mortality, picking out the young and fit before their time, and leaving parents bereaved and desolate. The influenza epidemic behaved in similar ways, and thus seemed to many to be a by-product of the conflict. The war had promoted the mass movement of peoples, so enabling its transmission, as it had their concentration in factories, transports, barracks and trenches. The war, however, was, like the hunger which accompanied it, a phenomenon over which humanity had some control. That was much less true of the influenza pandemic, whose cause and course were – and in many respects still are – a mystery. Fatalistic acceptance could be easier than energetic resistance.