Iran was also at the tail end of 4-year, 3-sided war that killed around 2M people. The very fact that there's 1.5M people (!) leeway in the numbers tells you something about the state the country was in, and how difficult it is to attribute those deaths specifically to one thing like the flu.
Apparently Iran also had a high death rate for spanish flu.
From wikipedia:
> In Iran, the mortality was very high: according to an estimate, between 902,400 and 2,431,000, or 8% to 22% of the total population died.[67]
> -- https://en.wikipedia.org/wiki/Spanish_flu