The latest reports indicate that a torpedo fired from a North Korean submarine sank a South Korean ship with a loss 46 sailors. Whatever else one might say, that was an unprovoked attack, which has (so far) led to no reprisal against the perpetrators.
This was the largest cost in lives for a single incident, since the original 1950-1953 Korean War. That war was never resolved by a treaty, only halted by an armistice.
While diplomats always dither, I suggest that this incident demands real action, because of its egregious nature, and the magnitude of the death toll. The problem is provocative action by units of the North Korean navy, committed upon the high seas. So, the solution is that no units of the North Korean navy should be allowed upon the high seas, until their government changes its idiotic ways.
I rather doubt that the UN security council would ever do anything substantive. They have almost never acted responsibly, not since that original Korean war. So, it is the South Koreans and their allies that must act, on their own.
My suggestion: allow no North Korean naval vessel passage on the high seas, until the North Korean government acknowledges the sinking it perpetrated, and promises massive policy change. Period. No room to maneuver, no room to "save face". The penalty is sink-on-sight.
Then, the South Koreans and their allies must actually carry out this threat. The North Koreans will inevitably challenge such a declaration, and they must suffer for it.
Sinking surface ships is fairly easy; sinking submarines is more challenging. So, I think a US navy battle group or two must be committed to this, and they must be free to sink whatever they see. No questions asked.
Once they get their noses rubbed in it, I think the North Koreans may steer a different, less objectionable, diplomatic course. This will be true in spite of the megalomaniac idiot they have for a dictator, because he depends upon the North Korean military to stay in power. While extremist, those generals are not fools.
We will have to hurt them to achieve this result, though. We must be prepared to do exactly what I propose: sink the bastards. No half measures. No mercy.