Which epidemic occurred during World War I?

The correct choice highlights the influenza epidemic, which is one of the most significant public health crises that emerged during World War I. The 1918 influenza pandemic, often referred to as the Spanish flu, is estimated to have infected one-third of the global population, causing an enormous number of deaths worldwide, particularly affecting military personnel as they were living in crowded conditions that facilitated the spread of the virus.

This pandemic had a profound impact on both military and civilian populations, exacerbated by the movement of troops and the harsh conditions associated with the war. It was characterized by rapid onset and high mortality, particularly among previously healthy young adults. Understanding this historical event offers insight into the challenges of public health, pandemic preparedness, and the social implications of infectious diseases during wartime scenarios.

The other options, while significant in their own contexts, did not have the same level of impact during World War I as the influenza epidemic. Smallpox had been largely controlled by that time, measles outbreaks occurred but were not as widespread or catastrophic as influenza, and the bubonic plague was not a contemporary concern during this period.