It is really quite worrying that this is being discussed.
What lesson should we really learn, to me the obvious one is that we desperately need the UN Security Council to have more muscle.
North Korea should have been stopped from getting hold of Nuclear Weapons, history has shown us that they are very safe in a MAD environment when controlled by sane Governments. North Korea is not sane, never has been - not an adult country that can be trusted with Nukes.
The list of countries like this is quite long, but not overly so. Few societies manage to fail so spectacularly over such a long-period of time, although being communist tends to be a strong marker for this.
The next on my list is Pakistan, utterly corrupt country and culture with religious extremism thrown in too and an existential fear of India. Only then would we get to the likes of Iran.
However, surely North Korea shows that the sanctions process is very key over the longer term - Iraq, with hindsight, even proves that.
I do wonder now that the hell China is going to do in the current circumstances - after all without Chinese help North Korea would still be a peasant state instead of nuclear armed terror threat. It is hard to know as I guess there is potential for China to like the idea of the North eliminating its rivals in South Korea and Japan - equally though, in statecraft the Chinese operate effectively over decades and are useless when things have to be done over days or weeks. A tricky situation indeed, the US is out of the game now, as any sate is when threatened with MAD.