Economic sanctions would worsen the situation, if anything. Kim and his closest allies are a bunch of crooks who live off cognac and lobster and sanctions would only harm the North Korean people, the vast majority of which are in dire poverty and live off tree bark. They rely on Western aid to live as Kim isn't going to do jack to help them. If the West withdraws their aid, not only will a lot of innocent people be worse off and will die, this will also build anti-West feelings that Kim will capitalise on and make him stronger in his own country. The only realistic way of taking down North Korea without the threat of nuclear war or a Chinese retaliation is to build anti-Kim sentiments in North Korea and hope they perform a coup d'etat.

On the whole, Kim is not going to launch a nuclear weapon on the West. However, more likely, and therefore a greater danger, is that he will manufacture these weapons and sell them to terrorists or Islamist regimes who will then pass them onto terrorists. Terrorists have nothing to lose when using nuclear weapons and even Islamist regimes are threats as they're into this whole 'kill the West and win 44 virgins in heaven' bullshit, meaning they'll have little qualms over dying if they annihilate the West in the process.

However, the most obvious problem this nuclear test is going to cause is that it is going to regenerate the arm race. The international community was doing so well in these post-war years but not only do we now have to thank the British-American (and Polish) coalition for their interference in Iraq and Afghanistan in causing Middle-Eastern countries to seek arms, nuclear weapons and to back terrorist groups, but now the nuclear arms race is back on. No doubt the nuclear community will begin rebuilding its stores and several more countries will want to join the nuclear club. Nuclear arms are useless - we're wasting billions on pointless, poisonous measures that could be better used to combat disease and poverty.