WaffenVW,
I don't believe you've taken the time to actually consider the size and complexity of the US Infrastructure. If (I don't believe it will happen) a coordinated EMP attack on the US were to occur, the every aspect of modern life that we know of is shut down. Within a week, 95% of most people will be out of food. When that happens, lawlessness and the associated chaos of joe six-pack trying to secure food for his 2.2 kids will add to the chaos of those that thrive on it. Law Enforcement will be overwhelmed and the inevitable call-in of the US Military will not be able to control the situation.
Even if the rest of the countries decided to start helping immediately, it would be months before any meaningful supply could happen. Logistics dictate that response time. In that time, a major portion of the population will die. Either to starvation or the inevitable violence, many millions will die. As this death occurs, disease will become rampant. That will only hamper efforts.