So in my story, North Korea is secretly given advanced technology and resources by an organization who want to use them to stir up conflict around the world for their goal. Let's say their tanks are equal to Russian T-90 or Chinese Type 99, their aircraft are well maintained Mig 29 and Su-33. They have laser anti-air and DF-21D carrier killer. But their industry infrastructure remain unchanged. Their soldiers are no longer malnourished and mind controlled to obey the Great Leader. However, their generals did not have the chance to test new combat doctrine and are still the same ones who wear a chestful of medals. North Korea is ordered by their benefactors to attack the South. The attack is sudden and unexpected. If they chose to isolate Seoul and trap most of the residents and remaining officials inside, while sweeping through the coast to severe the connection between Seoul and Busan, how quickly could they progress against what America and South Korea have currently deployed on South Korea homeland? In this Alternative Universe, China and Russian decided that they won't support the North Korea and choose to allow America, South Korea to conduct attack close to their border.