Why go down the nuclear route?
Biological warfare is far more effective: you can make them all poorly, very poorly, on death's door or holding the door open for the next victim.
It offers a means of escalation - "Stop that or we'll give you the flu, and if you think that's bad.....don't sneeze 'cos we added a little something" - instead of simply laying waste to everything.
How effective would sowing the North Korea water supply with Viagra be?