I was involved in an infrastructure conference once upon a time, and when we broke up into groups to evaluate the importance of various infrastructures, EVERYONE came to the conclusion that electricity was THE most importance infrastructure, as all others depended on it.

Now, thanks to the Not In My Backyard (NIMBY) movement, all the electrical generation is way out in the sticks instead of urban or even suburban areas, where the actual load is. So there are long transmission lines and substations in relatively rural areas serving urban customers.

Most of Uncle Sam's military bases have their own generation and are far away from urban areas, but if you cut the power to millions of people, they would be demanding that Uncle Sam help them instead of chasing Bubba out in the sticks.

Food is another item that has a long supply line to get into the urban areas. Again the military has MREs and the like, but when there are food riots in the cities, that's going to take resources away from going after Bubba.

It would be really hard to fight against an armed guerrilla force in the US.