Not a pleasant thought ~ thousands of martyrs, oil rationing/price hikes(?) Mind you with the US advantage in technology they could take out most military infrastructure from a distance with cruise missiles or a bit of B52 carpet bombing. Lets face it Iran (pop c70m) at best gave as good as they got against Iraq (pop c30m) in the Iran-Iraq wars and Iraq's offensive capability didn't last long against the US led coalition. I doubt Iran's would fare much better. If the US could gain and hold the oil fields and destroy the nuclear capability... the mountainous areas I suppose would be irrelevant. Still wouldn't be easy, cheap or a final solution Edit: Last estimates put Iran's military spending at $6bn pa which is similar to Sweden and Singapore (neither exactly known for their military posturing) and approx 1/90th of the US.