Syndemic
The worst of the 20th century influenza pandemics was the 1918 pandemic, where between 20-40 percent of the world’s population became ill between 40-100 million people died. More people died of the so-called Spanish flu (caused by the H1N1 viral strain) pandemic in the single year of 1918 than during all four-years of the Black Death. The pandemic had devastating effects as disease spread along trade and shipping routes and other corridors of human movement until it had circled the globe. InIndia, the mortality rate reached 50 per 1,000 population. Arriving during the closing phase of the World War I, the pandemic impacted mobilized national armies. Half of U.S. soldiers who died in the "Great War," for example, were victims of influenza. It is estimated that almost ¾ of a million Americans died during the pandemic. In part, the death toll during the pandemic was caused by viral pneumonia characterized by extensive bleeding in the lungs resulting in suffocation. Many victims died within 48 hours of the appearance of the first symptom. It was not uncommon for people who appeared to be quite healthy in the morning to have died by sunset. Among those who survived the first several days, however, many died of secondary bacterial pneumonia. It has been argued that countless numbers of those who expired quickly from the disease were co-infected with tuberculosis, which would explain the notable plummet in TB cases after 1918.
Effects of war
Estimates for the total casualties of World War II vary, but most suggest that some 60 million people died in the war, including about 20 million soldiers and 40 million civilians. The Soviet Union lost around 27 million people during the war, about half of all World War II casualties. The largest number of civilian deaths in a single city was 1.2 million citizens dead during the 872-day Siege of Leningrad. Based on 1860 census figures, 8% of all white American males aged 13 to 50 died in the American Civil War. Of the 60 million European soldiers who were mobilized in World War I, 8 million were killed, 7 million were permanently disabled, and 15 million were seriously injured.