It began with "Patient Zero", a sick, dying training WWI American soldier who was hospitalized at Ft. Leavenworth, KS in and around March-April 1918 with some mysterious ailment and then died soon after, but not before infecting most of other sick, wounded soldiers in the infirmary at the time, and then proceeding to cross the Atlantic and infect, sicken and kill hundreds of thousands of Allied and Central Powers soldiers, officers, and civilians in war-torn countries in UK, especially terrain-ravaged and badly-maimed northeastern France, occupied Belgium, Germany, Austria, Italy and neutral nations like Switzerland, Portugal and Spain, where an uncensored press actually was one of the few Western nations telling the truth about the spread, intensity and extremes and potency of the H1N1 virus, therefore it got the nickname, " Spanish Flu" by Western media reporters, observers and later on, historians. The virulent, potent nature of the H1N1 virus sort of began to wither and loose strength by 1920-21 by the time it reached Far East, Japan, China and Oceania (Australia and New Zealand) so the death toll due "Spanish Flu" in those countries wasnt as high in that part of the world as it was in USA, UK, France and European countries. Plus, we didnt live in such a highly-interconnected, globalised economy and world back then so information and diseases didnt necessarily spread as quickly as lets say the novel Coronavirus-19.
Plus Guido, probably a lot of ordinary peoples lives mightve been saved or hundreds of thousands, if not millions worldwide wouldn't have gotten so sick if they had practiced commonsense hygienic techniques like washing your hands and bathing at least somewhat regularly.