North Korea has always made empty threats to the United States and her allies since the ceasefire of the Korean war. Kim Jung Un is a new leader who simply wants to prove himself and the United States has a new Secretary of Defense who refuses to let anything happen which he could be blamed for. The DPRK is at such a disadvantage that even posing to launch a nuclear missile at South Korean, Japanese, or American targets could leave their country in ruin. No one wants a nuclear war, and the UN will fully support whoever steps up to stop North Korea. This is the United States' big chance to prove themself after the controversial invasion of Iraq in my opinion. North Korea is on the verge of committing suicide by threatening the United States. I wouldn't doubt that some of the newer missiles in their inventory could reach Hawaii, and bases in Japan and Guam are definitely in range. The US Navy has many interception resources and a missile launched at US or Japanese bases could most likely be blown out the sky before it can cause any damage.
In the event that North Korea does restart the Korean War, it will be a drain on the world economy and will threaten the safety of millions of people in Southeast Asia. Hopefully the DRPK government will listen to their big brother China and stand down before their country gets glassed.