Well, I think the problem with the Korean Peninsula extends farther then just North and South. Hence, why us the International Community can just let those two countries run wild with war and such. Not to mention if the International Community did allow those two countries to fight against each other...as hard and mean as this sounds no one wants to take in work and take care of civilians; especially civilians that North Korea has. Also at the same time people will cringe terribly at the thought of having another Communist rundown country like North Korea.
And they haven't been "fighting" with actual military weapons and such in the last few years. This current incident is a 2 month thing since they sunk that Naval Ship.
Essentially what this boils down to in my mind is. Because I did this for you...you owe me a favor now or I won't help you type of setting. Hence, why I think they've been in a stalemate for like decades.