You should read that book as well. There is a well regarded theory that says that if a certain type of emp pulse was fired off above our atmosphere that it would only take three modest sized bombs to completely wipe out 90% of our electronic infrastructure. It has something to do with the atmosphere amplifying the effect of the pulse.
This was all explained by this study the military put together on the issue.
It's the little simple things you don't think about that would wipe us out. For example.... In this book they talked about how a very large majority of the town (small town in West Virginia) thought they could hunt for food, which they did but the game didn't last long and soon it was hunted out. There are just way too many people to support that now. 150 years ago the population could sustain much more hunting but as our population has grown we have relied on our food sources coming from further and further away. If you look at how much of Kansas, Nebraska, eastern Colorado and other parts of the Midwest supply the rest of the country it's insane. All of that food relies on vast amounts of rail, truck and shipping to get to everyone.
If there is no transport to places like Boston, NYC, California and the NW it won't be long and those people will starve. Honestly the MIdwest will probably survive better than the rest of the country but the population density is a lot less. Those of you in Chicago are hosed unless you can get out.