How about an EM pulse from another country? No casualties except for our beloved modern day convieninces (electricty, electronic gadgets, microwaves, televisions, computers, internet, cars, etc.).
I could see how this might be a serious threat, something that a terrorist might strive for. It would cause economic disruption on an unimaginable scale. North Korea could easily have US by the shorthairs. How does the US retaliate for this type of attack?? No one was killed, and reciprocating with the same kind of attack on a country that is still in the stone age as compared to the US would not achieve anything politcally or militarily for us. I think this is a big issue, and a big reason to have an ABM system that works.