Absolutely must-read article about North Korea by Nicholas Eberstadt, in an op-ed in the Wall Street Journal. A few highlights:

As the U.S. and its allies frame plans for dealing with North Korea in the aftermath of the recent sinking of a South Korean warship, political leaders must recognize that security will depend not just upon deterring Kim Jong Il today. Northeast Asia's future security—and America's—will be profoundly affected by the government presiding over the northern half of Korea in the long run.

For this reason, Korean unification—under a democratic, market-oriented Republic of Korea that remains allied with the U.S.—must be the ultimate objective. Today that looks like a daunting and risky prospect. But to paraphrase Churchill: Unification would be the worst possible outcome for Korea—except for all the other alternatives.

...

Then there is the potential for Chinese suzerainty. This notion has been floated by Chinese authors in recent years, in the form of "academic" but officially sanctioned studies that depict an ancient kingdom—conveniently stretching from Manchuria to the current-day Korean DMZ—which was once historically part of greater China. ... Chinese suzerainty might put an end to the North Korean nuclear threat. But it would change the security environment in East Asia—perhaps radically.

Immense pressures would build in South Korea for accommodating Beijing's interests. Depending on China's preferences (and how these were parlayed), accommodation could mean an end to the U.S.-South Korea alliance. Japan would find its space for international maneuver correspondingly constricted; continuation of the U.S.-Japan alliance could even look risky. Much would depend upon Beijing's own conduct—but a Chinese hold over northern Korea would have devastating implications for the current U.S. security architecture in East Asia.

It is in the context of the alternatives—not in the abstract—that the pros and cons of an eventual Korean unification must be weighed.

The North Korea Endgame (Wall Street Journal)