EMP

No, North Korea Can't Kill 90 Percent of Americans

Scientists have known about the threat of electromagnetic pulse (EMP) for decades. EMP is a burst of electromagnetic radiation sent flying through the atmosphere by a nuclear or thermonuclear explosion. This radiation gradually fizzles out, but electrical objects near the detonation can suffer effects ranging from simply being turned off to having their circuitry shorted out.

...Jeffrey Lewis, an arms control scholar, wrote in Foreign Policy in 2013, "(the) EMP Commission exposed 37 cars and 18 trucks to EMP effects in a laboratory environment. While EMP advocates claim the results of an EMP attack would be "planes falling from the sky, cars stalling on the roadways, electrical networks failing, food rotting," the actual results were much more modest. Of the 55 vehicles exposed to EMP, six at the highest levels of exposure needed to be restarted. A few more showed "nuisance" damage to electronics, such as blinking dashboard displays."