North Korea isn't as nuclear capable as people would think. The first test they did in 2006 was a subkiloton yield that is suspected to be a failed detonation. It was confirmed as a radioactive.
The second was larger than a kiloton, though what you may have not heard was that there were no radionucleotides detected afterwards (which of course would have been more prevalent in a successful test) which has led people to believe it was not nuclear in nature and just more of North Korea trying to flex their muscle.
North Korea is not a threat.