[Mr. Jeeves]

North Korea has told its key ally, China...

I think that's akin to: "An angry pit bull has told its key ally, owner Steve..."

The pit bull might be marginally less inclined to bite the man who gives it food every day than it is to bite strangers, but the man is always well aware the possibility of being attacked exists.

[TSgt]

I concur.

So how does the world let a madman slaughter his own people and threaten everyone with nuclear war?

People are going to die either way and are dying now of starvation and execution. The citizens of the world can resolve this or the madman, or his heirs, will.