The 1918 flu was insidious and sneaky in nature, which helped it to sicken more than one-fifth of the world's population at the time. All told, Spanish flu would cause the deaths of more people than any other plague-like illness in history. \" This photo shows a demonstration at the Red Cross Emergency Ambulance Station in Washington, D.C., during the Spanish flu pandemic of 1918. Learn more about the 1918 flu pandemic in \"September 1918: War, Plague, and the World Series\" by Skip Desjardin. Now That's a Misnomer The Spanish influenza wasn't Spanish at all.