Sigh...North Korea is at it again...

It has been reported that North Korea has successfully tested a nuclear weapon in an underground explosion. No radiation leaks, at least we hope.
I just don't understand how North Korea thinks that by imposing an economic sanction on them a year ago as punishment for counterfeiting US money that the US somehow poses a military threat to them. The US has not made any movement towards invading North Korea, nor expressed any interest in doing so. The US doesn't want to meet with them individually, but continues to call for a return to 6-party talks. It's clear that North Korea is developing this nuclear weapons program to put pressure on the US, but we shall see how the US responds. All I know is that I can see this thing continue to escalate. And it wouldn't surprise me if North Korea chose to use their bombs proactively rather than retroactively once testing and development were complete.