They want to show the world that they are a power that shouldn't be messed with and could wage a war at any moment. The problem is, is that they don't have the technology to produce any missiles that could actually cause any harm. I believe they will continue to test their weapons until they feel that they have been taken seriously.
North Korea open hostility towards South Korea, Japan and the U.S. needs to stop. They know that if they attack SK the response back will be more powerful then ever before. I am surpised China doesn't pressure them more on human rights as they are there sole providor besides Russia and dictatorship nations.
North Korea likes to remind the world of their continued power every so often, and the recent launch of the short ranged missiles is just another example of them "flexing their muscles." While precautions should be taken in response to this action, world powers can rest assured that this act was not the start of a war, but rather a scare tactic.
North Korea is like that kid nobody likes in school, not even the bullies, but he wants to be a bully himself. This country cannot feed its own people and the government only stays in power because of a disturbingly gross level of propaganda. Instead of taking care of its people, it uses what very little funds it has to act like a tough guy. Akin to said schoolyard misfit threatening people with a lighter.
North Korea has a very powerful military for its size and where it is. Not to mention the fact that North Korea doesn't care for anything. Under the whim of a dime, they will do anything they want to, and control anything. North Korea doesn't have much muscles to flex though, so they flex what they have. Its like me flexing my tongue.
In 2010, North Korea sank a South Korean warship, showing its willingness to act aggressively against its neighbors in violation of international law. It was a demonstration that North Korea's displays of military force were not mere posturing. As North Korea grows increasingly more isolated and impoverished, its danger grows. Desperation may lead this hermit kingdom to lash out in further irrational attacks.