Re: Korea
I think the safest thing is to do nothing.
Don't attack N Korea, don't even threaten them.
In fact, don't trade with them or have anything to do with them, and encourage China and Russia to do the same.
At the same time, make it perfectly clear to Tellytubby that America has assigned a large number of ICBMs and/or SLBMs to be directed at his country.
Put the ball in his court.
Even an idiot like him would not 'nuke' S Korea, Japan or America without cause. He must realise that even a single nuclear warhead hitting any of these countries would result in the complete obliteration of his own country.
After a while of continued military expansion, I suspect the same thing would happen to N Korea as happened to the USSR; economic collapse.
In turn, it is perfectly possible that disenchanted people of that country would rebel and cause an overthrow of the ruling class, quite likely with the support of the military.