Take the electric network out and you've taken everything else out.
Pretty much everything in a modern city needs electricity to work - the water distribution system is controlled and monitored by a room full of computers somewhere, food supplies are controlled and ordered via computers, same goes for fuel supplies (domestic, industrial and vehicle), hospitals, dental and GP surgeries, pharmaceutical supplies, literally everything you need to live relies somewhere along the line on electricity (bearing in mind you're not going to take your bow and arrow into the forest and supply your family with fresh venison every day in New York or London).
A couple of recce aircraft to find the sub stations and then a handful of strike aircraft with PGMs can shut down a modern city in hours.
Even if most or all of the above have UPS back ups, they only last for as long as there's fuel for the generators - once the electric is cut you only need to keep a couple of aircraft in the air hitting fuel trucks whenever the try and move and the back up plans are useless.