Those in refugee camps, those in barracks, those with irregular food supplies and those living in unsanitary conditions were in those positions because of war, which had forced them there; moreover, when they fell ill, they were treated in over-crowded field hospitals packed with a whole range of people with other diseases and attended by staff who were jaded, overworked and undersupplied. If the flu subsided, the chances were that another disease would take over and kill off the patient before they left the hospital.
Nobody is completely sure of the origin of the flu. While the first confirmed case of the disease was found in the United States – at Fort Riley, Kansas – it seems more likely that that was merely the first place to be tested. European sources have located the source of the virus as a troop camp in Northern France, in the heart of the battlefields of World War One, with the hypothesis that the strain of influenza migrated to humans from livestock, most likely pigs. Indeed, the latter pandemic in 2009 was known as swine flu because of its origins in pigs.
A later theory held that the origin of the pandemic was in the Far East, with Chinese labourers stationed behind the lines on the Western Front. A disease in Northern China detected in 1917 has been found to be very similar to H1N1.
What seems incontrovertible is that the movement of troops massively influenced the spread of the disease. Regardless of the source of the virus, the way in which it was discovered – in two military institutions – leads to the idea that the concentration of military personnel and the demilitarization that followed the First World War lead to an above average number of people moving from infected areas and carrying influenza with them.
It was unprecedented in modern human history for so many people to move such large distances in such a short time as happened during the First World War. That, plus the cumulative effects of poor food supply, which weakened otherwise healthy people, close quarters living, which exacerbates the spread of disease, particularly respiratory diseases and the influence of chemical and gas attacks on those affected, is thought to have caused what could have been a limited localised illness into a global pandemic.
Once it had moved from military zones to the civilian sphere, the effect was devastating. Statistics on the death toll are not completely accurate, but it is thought that up to 17 million people died in the British Raj, now India, some 5% of the entire population. In Indonesia, one and a half million people are thought to have been killed. In the Pacific, 13% of the population of Tahiti died within a month, while 90% of all Samoans were infected, with 22% killed within in 8 weeks.
In the United States, the disease spread like wildfire among the densely-packed urban poor, whose cramped conditions ensured that the disease moved on rapidly. Native Americans, who were already incredibly susceptible to the strains of influenza that arrived from Europe, were decimated, as were First Nations communities in Canada.