They turned it off.
No invasions, occupations or casualties. Just an agreement fulfilled on both sides: South Korea and its allies shipping the down payment on what will be 1 million tons of oil to impoverished North Korea in return for the shutdown of that renegade nation's last, if barely, functioning nuclear reactor.
It's not that the reactor, or others like it, couldn't be started up again, or that the impenetrable regime of Kim Jong Il isn't perfectly capable of playing many more rounds of atomic blackmail. But the civilized world got what it wanted -- an effective, if not necessarily permanent, end to North Korea's nuclear activity, verified by international inspectors. And they got it by making it worth Kim's while to do so, not by brutalizing his nation and its already long-suffering people into compliance.
Of course, like the threat of North Korea's nuclear program coming back to life, the threat of military action or increased economic pressure by South Korea and the other nations with power in the region -- the United States, China, Russia and Japan -- also remains. It is a maddening cat-and-mouse game likely to go on for years, with constant vigilance required.
But the American experience in Iraq proves that military action, as an alternative to diplomacy and favor-trading, can also be less than decisive. And much, much more expensive.
This problem is not solved. North Korea's troublesomeness, not only as a nuclear nation but as a criminal enterprise, counterfeiting money and running drugs, will remain a chronic disease to be managed for years to come. There will be no "Mission Accomplished," though there remains hope that, with Kim's passing, a new, more friendly day may dawn on the Korean Peninsula.
All we can do is ramp up the diplomacy, keep the menace to a minimum and, come the day North Korea petitions for admission into the modern world, resist any urge to gloat.