See http://www.cnn.com/WORLD/meast/9810/02/iran.afghanistan/index.html for how close it apparently came to happening; and see https://en.wikipedia.org/wiki/1998_killing_of_Iranian_diplomats_in_Afghanistan for some background.
What if Iran invades in sufficient force to wrest the major cities from the Taliban (with the help of the Northern Alliance, etc.) but gets bogged down the way the USSR and later the US did?
What if Iran invades in sufficient force to wrest the major cities from the Taliban (with the help of the Northern Alliance, etc.) but gets bogged down the way the USSR and later the US did?