News of the artillery exchange between the two Koreas came as a shock. The world deplored the loss of life and is seriously concerned about further developments. It is important both to understand the reasons for the hostilities and to ensure they do not recur.

As far as we can tell, the ROK fired the first shots into disputed waters, disregarding earlier warnings from the DPRK, and the latter then "retaliated". This seems to have been the sequence of events.

For long time, the two Koreas have dreamed of unification. But they differ profoundly on the terms under which unification will be accomplished. The 1953 armistice ended open warfare, but half a century later neither a permanent peace, nor even a clear demarcation of territory, including territorial waters, has been agreed. This has sowed the seeds of discord, and armed conflict is prone to erupt at any time, either intentionally or unintentionally.

If both sides restrict themselves to insisting on their respective claims to these troubled waters the worst that can happen is a wave of antagonistic rhetoric – bad enough, but falling short of military confrontation. But if either side actively asserts its claim by force, it risks provoking serious military conflict.

This was clearly what happened this time, as on many previous occasions. Obviously the ROK side has the right to stage military exercises on its own territory. And if the area where the ROK's shells fell had been indisputably a part of Seoul's territory, it would have provoked no hostile response from the other side. But given that the ROK and DPRK have been in dispute over the waters for decades, and the DPRK had already warned of the consequences of ROK artillery fire in the area, it was rather unwise to proceed.

By shooting toward the DPRK, the ROK armed forces on the Yeonpyeong Island tested, unnecessarily if not provocatively, the credibility of the DPRK's deterrence. Since the ROK was not in a position to defend against the shelling, it begs the question why it chose to play such a dangerous game. Firing shells into disputed waters is not something to be done lightly, and testing the DPRK's stomach for a fight is reckless.

Having said this, "retaliating" against islanders, rather than firing into ROK waters, was far more than was necessary. After all, the ROK barrage only endangered marine life on the DPRK side. But the DPRK seemed to deliberately strike against human lives, which was completely excessive, disproportionate, and outrageous.

Even allowing that the ROK ignored the DPRK's warnings and infringed Pyongyang's sovereignty, the ROK at most caused some damage to marine life. If the DPRK felt it had to teach the ROK a lesson, it would have made sense to retaliate in kind by destroying marine life in ROK waters.

Striking against people on Yeonpyeong Island was an overreaction. Although the ROK failed to heed the DPRK's warnings, it hurt no human beings in the North. But the DRPK's artillery barrage claimed the lives of several people. This is why the DPRK action has been so widely condemned.