N Korea is a literal hornets nest. A gigantic, literally brainwashed army + nuclear arsenal + military "intervention" = nuclear war.
They can't even hit Japan.
The only way to attack the US is to nuke US military assets in south korea, or their major cities to provoke us.
Which could be suicidal for them.
It's already been revealed that Obama had their missile systems hacked which accounts for most of their launch failures seconds after initiation.
I highly doubt they'd get a nuke off before we crushed their capabilities with our military if we chose to.
The US could literally end their reign of terror and worse-than-national socialist styled hard labor / torture camps.