I've talked before about how nuclear disarmament, like total nuclear disarmament, is going to happen suddenly.

Not because the missiles launch or because someone cracks the diplomatic code to get North Korea, India, Pakistan, China, Russia, Israel, France, the UK, and the US all on the same page, but because countermeasures developed enough that someone is able to make a complete decapitation play to try and get an early lead on the post nuclear game for primacy.

It will go down in history as the war of 30 seconds, because that's how long the mass strike on all the nuclear capabilities of the aggressed and their potential nuclear allies will likely be cut down to.

As for what the ultimate nuke killer in question will ultimately be. I would bet heavily on high speed long operation time drone tech. Build enough drones that can stay in the air for days or weeks or even months, make them fast enough, and all you would need is enough intelligence gathering to identify all the targets.