The last true worldwide pandemic infected about 30% of the then world’s population of 1.8 billion in 1918 and killed millions with some estimates as high as 50 million. It was called the Spanish Flu because Spain was the only country truthfully reporting the infection and death rates. Other countries were still fighting WWI and didn’t want the enemy to know the true extent of the virus’s impact while Spain remained neutral in WWI.
The Spanish Flue was a Swine Flu and it spread among troops who were often in cramp conditions on military bases. It decimated whole military bases and with troops being moved and stationed all over the place, the virus was spread throughout Europe. The virus found its way to the rest of the world just because of the sheer number of infected and the lack of knowledge about viruses and how they were spread.