Just a few months earlier, the US military had faced a wave of influenza that struck a base in Kansas, now believed to be an early incarnation of the Spanish flu — so-called because of an assumption, at the time, of its country of origin. It had spread rapidly but was mild, resulting in relatively few deaths before petering out.
The 1918 flu was widespread in Europe, but reporting of it was suppressed as “detrimental to the war effort”. It was not until the flu reached neutral countries, ie. Spain, that that reports began to emerge. Thus it came to be knownas the Spanish Flu.