I used to be more critical of North Korea directing so much of their national output towards their military. My idea was that this was a false economy, and that building up their civilian sector would have expanded their national capacity at a pace where they would end up with more military capacity.

I see now that:

They actually did make an effort to do that. but the collapse of the communist bloc and US sanctions made a long period of economic contraction inevitable.
The North Korean state would have likely been invaded or bombed if it had not maintained a credible military deterrence. It's notable that they have never been the target of serious military action since the Korean War ended.