Could a war with Iran affect stock markets?

Stocks will go down if, and when, there is a long war right? At least that is what many people worry about, given the situation with Iran and the US right now. That is what many believe, but is it true?

Let’ s look at a long- period of time — over 90–100 years — and see if wars have had an impact on the natural trend markets were having before the outbreak of wars.