But here is one method the NK could use to make trouble and maybe think they could win.
From Israel Nation News at: http://www.israelnationalnews.com/Articles/Article.aspx/13044#.UVYqb5P-EwB
QUOTE: Published: Sunday, March 24, 2013 3:03 PMEven a small, relatively crude nuclear device detonated above the Korean peninsula would generate an EMP with field strength well above 10 kV/m, ensuring wholesale destruction of unprotected electronic systems. UNQUOTE
So a NK game-plan could be to explode such a device over South Korea and perhaps one over Japan, and in the ensuing communication black-out send its very large but relatively primitive army rolling into South Korea.
I am not military expert, so I'm totally in the dark as to whether such tactics can work, nor do I know whether US military technology can protect US military communications. But, if the Israeli concept can work, then the the only practical reaction of the USA is a devastating bombing attack on NK and the probable death of millions of NK people.
Not a pleasant choice.
And for NK, its looks like a Jim Jones moment.