Rogue nations (such as Iran or North Korea) might create a high-altitude nuclear explosion that will emit EMP (electromagnetic pulse) which will instantly fry and knock out our delicate hi-tech electronic equipment and power grid, plunging us back 300 to 400 years.
William Forstchen has written an eye-opener fiction novel titled "One Second After" depicting the chaos and the anarchy caused by an EMP strike with no electricity, no running standby generator, no clean water, no water treatment, no sewage treatment, no running automobiles, no food supply, plane crashes, no telecommunication, etc.
This is scary warning.