This is what we do: 

Assemble all of the top commando teams from the free world. Using intelligence from satellites and any other reliable sources, assign a team to each weapons system currently set up to hit Seoul. Place submarines off the Korean coast with enough non-nuclear missiles to wipe out all missile silos. Save a few as a hello gift to Li'l Kim's personal compound. Send the commandos in. On a set time, blow all the weapons aimed at Seoul, and at the same moment fire the missiles. The silos will be destroyed without any ability to retaliate against Seoul. Have bombers and jets ready to wipe out any Army units that attempt to cross into South Korea. 

Neither Russia nor China will go to war over Korea, as they know Korea has threatened the national security of the US.