Contrary to the name, which is simply a matter of wartime secrecy resulting in it not being publicized before arriving in Spain, the Spanish Flu most likely originated in or near Kansas in spring of 1918.
The pandemic is conventionally marked as having begun on 4 March 1918 with the recording of the case of Albert Gitchell, an army cook at Camp Funston in Kansas, United States, despite there likely having been cases before him. The disease had been observed in Haskell County in January 1918, prompting local doctor Loring Miner to warn the US Public Health Service's academic journal. Within days, 522 men at the camp had reported sick. By 11 March 1918, the virus had reached Queens, New York. Failure to take preventive measures in March/April was later criticized.
It was then spread to Europe by U.S. military deployments to France.
No-one knew at the time of course, that the new flu was going to be so deadly,; or greater precautions would have been taken early on.
However most new influenzas originate in Eastern and South-Eastern Asia, do to the very close proximity with which the inhabitants there live to both swine and ducks. This facilitates cross-species jumping and adaptations of the viruses. Hence the prevalence of the terms swine flu and avian flu. This is certainly true for several of the major flus of the past decades: