North Korea tested a nuclear bomb. Click on that link if you want to read the about the test itself--I'm more interested in the fallout.
Even though the test device was detonated in a 700m deep shaft, radiation will still escape into the atmosphere. And the US Air Force WC-135 Constant Phoenix is surely already busy flying off the coast of North Korea performing their dull but essential particulate analysis mission. This will likely confirm that the fissile material was the product of NK's Youngbyon reactor complex.
Now what? The fears are that this will spark an East Asian arms race. Japan has all the necessary technology and plenty of nuclear facilities to leverage--they could build a nuclear capability very quickly if so inclined. With new PM Shinzo Abe at the helm, and the pacifist voices of Hiroshima and Nagasaki survivors growing more quiet by the year, this is a very real concern. With Japanese deployment to Iraq (albeit in a nominally non-combat role) passing without major controversy at home, the groundwork for rearmament is already being laid. Japan's dependence on imported energy sources may prove to be the final straw--will Japan be able to curry favor abroad and continue to win oil concessions through charity, or will they feel the need to back that up with a military stick? While oil is theoretically fungible and traded freely worldwide, there is simply not enough oil within easy reach of hungry East Asian markets--as effective as charity may be, it is not capable of forcing open a choke point such as the Strait of Mollucca.
In addition, one of the long-standing Korea theories holds that the ultimate goal of America is to maintain the status quo--a divided Korea is stabilizing because it prevents either regional unification or conflict. Specifically, a divided Korea keeps a powerful US military force--and just as importantly a viable excuse to maintain that force--in the theater. A divided Korea provides the justification for the US to remain as the military protector of Japan, and thereby prevent their re-armament. So long as a US military force is committed to the region, and opposed to China, Japan does not have a reason to build up its own "Self-Defense Forces" to counter a chinese threat. Or so the theory goes. But with the US bogged down in Iraq, further tied down by the need to deter Iran, the US military presence in East Asia rings hollow. In my opinion, there is no viable military option available to the US. And so far, the Bush version of diplomacy has failed both locally (it didn't prevent this test) and globally (it has shown nations such as Iran that you will be handled more softly if you already have the bomb). Would the Clinton version--direct engagement and talks--be any more successful? I think it would be more effective locally but equally counterproductive globally--it still shows others that you get what you want when you play the nuclear card. Either way, it will be interesting to see what will happen next...