I think the threat is minimal to america they have played this card for many years its a great way to feed your people(and line the pockets of politicians) when you are a underdeveloped country they threaten we send food. I think Kim is posturing for his people to prove he is a strong leader and brave and willing to take on the US.......but unlike the US who sent bombers from US to South Korea and back in a mock drill (show of strength) he has no way to to do anything close to that. I would not worry :)
No, most likely North Korea is just threatening America to get what they want. I lived on an American military base in Korea for two years. We got many North Korean bomb threats, but they never went up with their threat. So don't worry.