North Korea is trying to put on big boy pants and be seen as a real threat. While most of their population is malnourished, China their only ally is starting to get pissed off with their bullstuff, and their military consists of poorly maintained soviet era technology.
The worst they could do is rain down a ton of shells on South Korean civilians for a few minutes which will effectively wipe them off the face of the globe, since no country would deem it acceptable. It would probably end up with quite a sizable South Korean civilian death count. However there would be the huge problem of what to do with the population of North Korea.
where do you do your learning
* comr4de squirts with water bottle
bad BAD BAD
while a lot of their military uses older technology that does not mean that their weapons are ineffective. Guns still shoot and guns can still kill people. North Korea is a threat to everyone on that peninsula, which just happens to include about 28,000 US soldiers. If there are ANY americans threatened by NK it's them.