Hi Tom,
According to Daniel Pinkston (a very smart analyst in Seoul) North Korea probably sees the "Foal Eagle" military exercises plus latest UN sanctions as similar to the workup towards invasions of Afganistan and Iraq. Hence the more serious sabre-rattling this time.
Hopefully somebody will confirm that the US isn't planning to invade North Korea or nuke it, and things can settle back to their bizarre normality. Otherwise if Foal Eagle concludes without an invasion, North Korea can congratulate itself for heading off nuclear catastrophe by presenting such a brave front.
Check out what Senator Menendez had to say about the threat- the word he uses is "absurd".
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1
