Well read the wiki artical
Nukes behave alot different in space. I am no expert but they are very different in space and behave more like solar flair does. Alot of it just dissipates harmlessly and does trash satelites.
EMP is a problem for any country.
EMP the ultimate breakdown of civilization? Hardly.
I mean OK, lets just go into fantasy land. Russia is back or China and they have nukes. You think they want to start a war by opening up with a couple stupid EMP bombs in space? I doubt it.
Mutually assured destruction is one fuck of a deturant. I kinda doubt that would be the opener.
It certainly would not be my opening move in a global war.