North Korea has every reason to believe that Red China will back them up, should they ever get into a battle with the US. Japan is very, very nervous right now.
North Korea may just be waiting for us to spread ourselves too thin in the Middle East, before they decide to take South Korea and Japan.
And I have no doubt that they will use their nuclear arsenal, if it looks like we may keep them from getting what they want. Totalitarian regiems do not hesitate to use "Scorched Earth" policies.
"North Korea may just be waiting for us to spread ourselves too thin in the Middle East, before they decide to take South Korea and Japan."
South Korea, probably - but take Japan? How the hell would they do that?