After reading through the thread I feel I need to highlight some logic behind modern strategic warfare.
The main thing is the idea of using a single weapon to take out a country was just cold war fear mongering, the reality is somewhat more logical.
For example, if you are going to spend funds in taking out a country, unless you have an uncontrolled hatred (the only example of this is between Pakistan and India, I spent 7 weeks in India and they utter hatred between the two countries truly shocked me), you would use a yield that would take out the defence but leave the resources for occupation.
the obvious solution is to use a low yield warhead (50Kt approx.) detonated 200 miles up, that would give a maximum EMP burst that would take out the whole of the UK (for example), and by sending multiple missiles you only need one to be successful. This would render all electronics useless, disable comms, fuel, water, waste.... basically everything you use on a daily basis, this would also yield minimal fallout and enable a ground force quick victory (if they wish to do so).
The direct impact on us Preppers is that you'd need analogue solutions for basic survival, along with electrical equipment stored in a faraday cage, and the faraday cage will need to be perfect.
as I've stated in other threads, I'm building (and have been for a very long time) a bunker, not really for any reason but to understand the logistics and something to keep me out of my wife's hair and not get myself into trouble
With an EMP attack, you will have many stages (taking the actual war out of the equation), firstly would be the immediate lack of power, comms, and mobility (unless you have a very old vehicle, bicycle, or horse), the next stage will be a lack of fuel, water and removal of waste (main drains will quickly back up), then you will be getting to the stage of hunger, disease (infected water, lack of medicine etc) then finally all out survival, and this would happen all within the first 30 days.
Why destroy a country when you can get a country do it to itself, then you go in as the heroes bringing supplies, restoring utilities etc.