How do you get the Kessler syndrome going?
It's actually something you'd have to spend a lot of resources to create in the first place. Launching tons of little impactors in polar orbits at varying altitudes would probably be the least expensive way. You'd basically want a belt of impactors crossing East-West orbits to give the maximum opportunity for impact events.
Small steel ball bearings would make good impactors I think. Most satellite buses are aluminum so steel would tear them up pretty well and would be more likely to shatter solar panels. Being conductive there's also more opportunities to cause electrical shorts as they pass through circuit boards and wiring.
The main problem is you would need literal tons of them launched into polar orbit which would need a lot of fairly hefty rockets. Polar orbits are more difficult than other LEO orbits because there's no free velocity from the rotation of the Earth so that delta-v needs to come from propellant which means less payload. The delivery vehicles would essentially be space Claymores.
To the point of helping isolate commands in a Twilight War...I think anything short of simply taking away modern technology isn't going to do much. If GPS and DSCS/GBS/WGS disappeared tomorrow it would annoy but not necessarily cripple any first world military.
HF radio would still exist and work fine, as would compasses and AGPS systems and all manner of aeronautical and maritime navigation aids. INS would also still exist so most weapons would continue to work as well since they're not wholly dependent on GPS to deliver long distance booms.
Computers add a great deal of capability to low bandwidth communications. Relatively unsophisticated radios attached to off the shelf laptops can be comms workhorses. I'm sure headquarters and signals units have non-satellite comms gear that puts ham stuff to shame.
I think the real breakdown would be in civilian infrastructure that relies on GPS and other space based systems. For instance a good deal of synchronous networking uses GPS to keep clocks adjusted.