Iran has in the past put the world on guard that it would close the Persian Gulf to shipping if it were attacked. The impact would be huge. Americans mostly would feel it at the gas pump, with oil prices soaring out of control.[nationaldefensemagazine.org]

One of the down-sides of being authoritarian douche-bags is that the minute we cut your heads off, all your citizens will go "Here, lets us help you clear the straight of Hormuz and get that oil flowing again."