North Korea today can threaten all of South Korea and parts of Japan with its conventional missiles and its conventional military. The North can fire 500,000 rounds of artillery on Seoul in the first hour of a conflict. Stability has held for 60 years because the U.S. security alliances with South Korea and Japan make it clear to the North Korean leadership that if they attacked South Korea or Japan, they would lose both the war and their country. And, for half a century, neither side believed that the benefits of starting a major war outweighed the costs. The worry is that the new North Korean leader might not hold to the same logic, given his youth and inexperience.
Further, the NORKS are willing to sell what they have - essentially nuclear technology and missiles to other regional "bad boy" countries.
Point taken, the DPRK as a regional threat should not be taken lightly, especially if you happen to live, say, in South Korea. And, down the road, they could get worse.
Right now, the NORKs could kill a lot of South Koreans and rip up parts of South Korea - for a little while.
Unlike in the 1950s, the South Koreans today are not unarmed and unprepared. Nor are they without allies.
On the other hand, the DPRK is not part of a powerful alliance. It has trouble feeding itself. It has no oil and gas to sustain lengthy military operations.
Will the NORKs foolishly count on the Chinese to save them again? Why would the Chinese do that? Other than regional hegemony, what dog does China have in a fight between the DPRK and the ROK? Clearly, China has moved on from the 1950s. Will China recognize that the DPRK is the past and not the future?
Would Russia intervene on the DPRK side? Why? Well, they share a border.
Can the DPRK look to its "friends" ("customers" is perhaps a better term) in the world? Like Pakistan, Iran, Syria?
Will the great Iranian fleet sail to deliver sustainment goods? It's a very long trip, isn't it? What would be the risks to a fleet carrying goods to an outlaw state at war with the rest of the world?
Syria seems to be preoccupied.
If the DPRK should unleash its forces, what does it do? Shoot off all of its rockets and artillery and kill lots of South Koreans and perhaps some Japanese? For what purpose? Might as well smack a hornet's nest.
Does it invade the South as it did in the 1950s? And then what? Can it sustain its army in the field or will it be rolled again as its supply lines are cut? Will it attempt to live off the land?
Will it try to nuke the U.S.? To what end?
It is good to acknowledge that a lot of artillery tubes, some rockets and a large army are a threat.
It is also good to think about what the DPRK sees as a desired end-state should it unleash those forces and whether there is any possible way for it to get there by destroying itself - which is surely the most likely result if it takes action.
Is the current Kim-in-Charge really so young and naive as all that? Is he willing to, in effect, commit his country and himself to a suicide path?
UPDATE (3/30/13): Nice piece in The American Spectator by George H. Wittman, "Peace Through Bluster and Missiles" on the DRPK's possible motivations in rattling their sabers. Note the EMP threat of a NORK aerial nuclear blast.