N. Korea is state version of al Qaeda. A master of terrorism before Muslim Jihadi came along. Their whole warfare is structured to be large effective terrorist force, also equipped with biochem weapons, nukes, and array of ballistic missiles.
Gone are large conventional Soviet-style NK military which had its heyday back in 70's or early 80's, which collapsing NK economy can no longer support and outmatched by growing S. Korean conventional military. They still maintain large military but much of them are no longer effective fighting force.
That is why The DPRK have also been in contact with Middle Eastern terrorists in learning IED technologies from them, if push comes to shove and they are overrun by the ROK and US in a joint offensive effort on the ground after massive bombing (and if also joined by Japan and others in such an occupation); they are hardened for a long, drawn out nasty guerilla warfare with tactics they saw working in Iraq and Afghanistan by jehadi.