Final answer:
The deadliest influenza pandemic occurred in 1918-1919, known as the Spanish Flu, resulting in the deaths of 50 to 100 million people worldwide. It was exacerbated by World War I conditions and affected military and civilian populations severely.
Step-by-step explanation:
The 1918 Influenza Pandemic:
The most lethal pandemic of influenza in history occurred in 1918 through 1919, commonly referred to as the Spanish Flu. This pandemic claimed the lives of an estimated 50 to 100 million people globally. While it was named after Spain, the disease likely originated in the United States. The conditions of World War I accelerated its spread due to crowding, poor sanitation, and the massive movements of troops and animals.
Vastly more lethal than typical flu epidemics, it killed a significant percentage of infected individuals, with a profound impact on both military and civilian populations. The pandemic came in multiple waves and had a significant impact on society and the economy, leading to massive loss of life, overwhelming medical services, and disruption of everyday life. In the end, it took several years for the pandemic to subside, with no effective cure found during that time.