Metro News reveals just how devastating an EMP (electromagnetic pulse) attack could be to the US.  Also, based on this article, you
should worry more about EMP warfare than nuclear war.   Granted, this article is based on North Korea being an aggressor.  Hopefully, with the recent turn of events, North Korea is soon to be no longer a threat. But, how long will it last?  Also, Russia has continued to be aggressive.  So, the US needs to be ever vigilant.

If an EMP was fired over the US, it would not only devastate the electrical grid of a country along with all its infrastructure but this would lead to widespread casualties. What is an EMP attack and how to prepare for one | Metro News

A former CIA director is also worried about the damaging effects of an EMP attack:

Former CIA Director James Woolsey has said that he believed this type of attack would cause society to collapse leading to a high number of American casualties. What is an EMP attack and how to prepare for one | Metro News

Obviously, the US and the modern world lives on electricity.  If we were to lose power suddenly, food would spoil, medical patients would suffer (I.E., most modern medical equipment would be useless),  and rioting would likely soon start.  The U.S. could literally be put into the stone age overnight.  What is most frightening is that EMP weaponry does not need to be as accurate as traditional ICBM missiles.

Using the EMP as a weapon may be desirable for North Korea as it requires less accuracy, and an EMP blast could affect a 700-mile radius (1126 km).

The only spot that will be unaffected will be the small area exactly under the explosion close to the ground where the Earth’s magnetic field will create an eye of the storm.

The EMP would only need to hit a general area of the target to cause significant damage. What is an EMP attack and how to prepare for one | Metro News

What can you do to prepare?   This article gives good, general advice, on how to prepare for an emp attack.  For example, food supplies will be decimated.   Many tips given are mostly the same tips that you would give anyone for traditional disaster prep.   But, one thing you should look into is a Faraday Cage.

This is a metal box that is designed to protect item inside from an EMP attack although the effectiveness of it depends on the magnitude of the strike.

You can make a Faraday Cage from old microwaves, metal filing cabinets, and aluminum cans and insulate with cardboard for added protection from the elements. What is an EMP attack and how to prepare for one | Metro News

This is a good read and recommended for anyone who is interested and unfamiliar with the dangers of EMP warfare.