In OTL, North Korea is not just a Stalinist dictatorship, it's an insane Stalinist dictatorship. AFAIK, this change to "insanity" was ingrained around the time Kim Il Sung died, and is also when North Korea really fell apart economically. So with a POD of, say 1986, what events could lead the DPRK, without reunification to do better than OTL?