The President recently noted that getting diplomacy on one page with Russia, China, South Korea, Japan, and America all struggling to agree on an approach to North Korea is time consuming.
It is difficult. This article discusses why our military options are not viable as a step to solve the problem right now (if war breaks out from accident or North Korean desperation, that's another matter--then we certainly can destroy North Korea).
The threats each of the five face from North Korea derive from the different points of view.
Look at South Korea. They seem annoyingly unconcerned about North Korean nuclear weapons and long-range missiles. Sure. The North Koreans and their Chinese allies captured and destroyed Seoul--where a quarter of South Korea's population lives--twice in the Korean War. And since then the North Koreans have had an army poised to launch an offensive to capture the city a third time. Even though North Korea's army is declining and South Korea's is growing more powerful, the North Koreans retain large numbers of tube and rocket artillery within range of Seoul that could turn the city into rubble without even crossing the DMZ. So North Korea getting a few nukes is rather irrelevant. North Korea doesn't need nukes to wreck Seoul.
And then there is the possibility of winning. What if something happens and North Korea collapses? Will South Korea have to step in and spend the money to build northern Korea up to ROK standards? Sticker shock is an understatement. They've seen what West Germany had to spend for a far better off East Germany. South Korea wants North Korea to exist, stop being a threat, and slowly catch up with South Korea economically. And then let South Korea absorb them. Good luck with that foreign policy goal!
Of course, with American forces deploying away from the DMZ, the South Koreans may get increasingly nervous that large numbers of Americans won't die in the opening hours of a North Korean attack. This would Leave South Korea a little more exposed. South Korea might change their positions to account for this.
Then there is Japan. They seem the most insistent on doing something. They have a harshly worded UNSC resolution in hand. They are building up missile defenses and their military capabilities in general. They are working closely with America. Why? Well, North Korea already has missiles that can reach Japan and if the North Koreans can weaponize a nuke and put it on one of those missiles, Japan might have the distinction of being the target of the third nuclear attack in history. Japan does not have nukes so they rely on our extended deterrence capability to stay Kim Jong-Il's hand.
China is in a different position. In the past, North Korea was an ally and a potent threat to South Korea. Ah, those were the days. And days a decade gone and unlikely to return. So China has the choice of a shaky North Korea that can at least threaten with nukes or a collapsed North Korea that South Korea might occupy. North Korea isn't going to attack China. And if North Korea collapses, North Koreans will flee to China as refugees. That will be expensive. Not a killer since China is so large, but they'd rather not pay.
Then there is the sheer joy of having a loosely aligned loose cannon giving their potential foes America, Japan, and South Korea fits. It is hard for China to put away this deadly weapon that threatens us. Who knows, maybe China will get lucky and North Korea will harm Japan, South Korea, or America without anything spiraling out of control to harm China.
But there is also the danger that North Korean pursuit of nuclear missiles will prompt Japan to go nuclear. A nuclear-armed Japan would be a disaster for China. And will Taiwan go nuclear next? And South Korea? Really bad. But the dream of a North Korea that threatens the continental United States is too sweet to abandon now. China is on a tightrope.
Russia is kind of the odd one here. They have a small border with North Korea so refugees aren't much of an issue. Russia doesn't want to annoy the looming Chinese by opposing China too much. Remember, for the foreseeable future, Russia's Far East is not defensible short of using nukes against a Chinese threat. Yes, Russia gets a little thrill from seeing America squirm but Russia really doesn't want us to fail and leave Russia to face China alone. In the end, Russia is there in the talks by courtesy and proximity, I think. I don't see what dog they really have in this fight other than the wish for general stability in their region. They probably wouldn't cry too much if North Korea did harm us, Japan, or South Korea without catapulting China to regional hegemony.
Finally, there is the United States. We are driving this whole thing to stop North Korea from being a threat. We named them a charter member of the Axis of Evil.
We are least under threat from North Korea so far and want to stop North Korea before it can threaten us directly with nukes. We have the advantage that we may be able to build defenses to stop a small attack from North Korea at short, medium, or long range. We have the advantage of having lots of nukes and so can hopefully deter Pyongyang in all but the most delusional state of mind. We don't mind if North Korea collapses since we won't have to pay for it directly. We can live with a conventional invasion of South Korea since we are getting out of the way and South Korea can largely handle it with our air and naval power in support of their army. We are working on blocking North Korean nuclear and missile exports (including intercepting ships at sea) and are cracking down on North Korea's criminal enterprises.
We can also afford to play harder ball than our South Korean and Japanese allies. So other players who fear collapse or war or small attacks close by have to play along with us than they might like since we can push things much farther without any really bad effects hitting us--at least compared to the rest of the five.
We can never agree on a common plan that addresses all of our security needs. But this suits us just fine, I think. We want an excuse to avoid a deal and failure by all five states to agree on a common plan provides this excuse to simply contain North Korea and continue to squeeze them. And this "doing nothing" lets North Korea slowly die.
Yes, a collapse will be expensive for South Korea and China, but why should we care? Those two don't seem to worry about Los Angeles being threatened by North Korean long-range missiles in several years time.
In the end, we must look to our interests just as the others look to theirs.
Besides, as much of a problem that North Korea is with perhaps a few nukes (but no ability to launch them on missiles yet), Iran is the threat we must focus on. Iran has nuclear ambitions and is a prime terror-sponsoring state deluded by their own form of jihadi fanaticism.
And like I always say, better to go after the nutball regime with no nukes to stop them from getting their first nuke than go after the nutball regime with nukes to disarm them.
UPDATE: Austin Bay describes elements of the "python strategy" to squeeze North Korea. I always assumed the Proliferation Security Initiative was part of this strategy.