Technically NK declared the armistice that was signed at the end of the first war was null and void on March 11th. They have been rather overly dramatic about it making me think they're very afraid of the consequences and are half-hearted to committing to an attack or they have a trick up their sleeve that they've kept secret very well (don't think this one is likely but still possible).
[Edited by Neo7, 3/29/2013 8:41:50 PM]
This seems appropriate..
Link
they will start the war only if china permit them
IIRC China recently said they can't control North Korea anymore.
It's a risky situation there, to say the least. If NK attacks SK, Americans will join in because they just have to interfere with everything, which means China will interfere as well. Meanwhile Russia won't do a thing cause they're not on good terms with China even though they're both Communist.