North Korean makes threats to get bribes or payoffs from other countries like South Korea, Japan and the US. They have been doing it for years. The people are shrinking in height (averages) from undernurtrition.
North Korea may attempt to threaten the United States, but there won't be a World War brought about from these current events. It all goes back to the Korean war in the 1970's, when the U.S interfered with Korean affairs. They just feel the need to make false claims of having powerful weapons to try and scare the U.S government.
This earth will not be destroyed completely by any nuclear warfare. The earth was made to stand to "time indefinite." - "Psalms 148:3-6- Praise him, YOU sun and moon. Praise him, all YOU stars of light. ?Praise him, YOU heavens of the heavens, And YOU waters that are above the heavens. Let them praise the name of Jehovah; For he himself commanded, and they were created. ?And he keeps them standing forever, to time indefinite. A regulation he has given, and it will not pass away."
I don't believe it will happen. The United States is one of the most powerful countries in the world. The US also has many allies as well as enemies. But other countries by now know that there threats against the US, better just be hollow words.