Well, there have been a lot of things created due to war. Things that people take for granted, like GPS.

However, there is a theory, that there have been at least one or more periods of advanced civilization in Earth's past. The theory believes that humans got to a certain point and then did so much destruction, that civilization had to revert back to hunter-gatherer stage. If EMP bombs were detonated, it would destroy the electrical network for the USA. It would probably do the same for other countries. Developed countries cannot live without electricity, because we are too dependent on it. It would take 6 months to a year to fix and in that time, civil unrest would destroy any chances of getting done.

Of course, the EMP doesn't have to be from NK. It could be a solar flare CME (coronal mass ejection). One launched yesterday, that if it was more pointed at the Earth, would have knocked the lights out.