An EMP event, whether caused by solar activity or enemy attack, would destroy our electrical grid, effectively cutting off power to the country, destroying communication abilities, grounding airplanes, making automobiles and trains inoperable.
This would disrupt virtually everything most Americans need for daily survival including food delivery systems, hospital services, supplies of needed medicines, water delivery systems, refrigeration, cell phone/landline phone services, emergency services, food refrigeration, home heating and cooling, television, computers, generators, etc., resulting in massive death.
For a relatively insignificant amount of $500 million, the nation's electric grid could be hardened against an EMP event. See H.R. 2417.