Grover floats an idea:
Now assuming that the incident was the product of centralized decision making rather than an unintended one ordered lower down the food chain (something I discussed earlier here), Kim Jong Il may simply be engaging in a tit-for-tat retaliatory strike for an earlier skirmish, something the Times itself suggests. And while such a diversionary war would likely distract at home and provide some temporary relief from any internal pressure, is the “Supreme Leader” really so risk acceptant as to start something that could spiral into a bigger war that could see his downfall?
My guess is that the incident was not intended to start a diversionary war but was either retaliation or another in a long history of provocative displays of force by the North Koreans. Then again, Kim Jong Il may be assuming – perhaps correctly given South Korea’s current lack of desire for a major war on the peninsula – that any South Korean response is likely to be quite limited and can provide some helpful distraction. Of course, this is all premised on the notion that we are talking about a substantively (or even procedurally) rational, unitary actor – something that might be a stretch in this case.
This is interesting, because South Korea really faces a quandary. War is simply not in South Korea’s interests. While it’s exceedingly unlikely that the US and South Korea could lose a war against the North, South Korea would nevertheless pay very high costs in both military and civilian terms. Moreover, in a general war South Korea loses even if it wins. Integrating a war/famine/communism plagued North Korea will be an enormously expensive and time consuming endeavor, one which Seoul does not particularly wish to contemplate. I suspect, then, that South Korea is willing to tolerate considerable North Korean aggression before resorting to general war.
The North seems to understand this, which is why a limited diversionary war seems plausible. Then again, it’s a very risky game for North Korea, and previous North Korean behavior has suggested considerable paranoia about US intentions. It’s unclear just how far Pyongyang would be willing to push Seoul and Washington in order to derive domestic benefit. I suspect that Grover’s second suggestion is correct; the North saw the destruction of Cheonan as an acceptable degree of escalation in the naval war off Korea’s west coast.