North-Korea has attacked South-Korea

The only way Seoul could be saved would be nuking all of NK at once(and even then it'd be hard). Except hardly anybody would do that, even if more people would be saved that way. Personally I would've done that a long time ago if I had the chance to(or just evacuate Seoul and the like then attack). Would suck for the people in NK that want to live a normal live(unless it's possible to take out just the NK military) but it's probably going to be the only way. Unless NK suddenly decides they've had enough of this stupid conflict and just wants to be friends.

Or send Jack Bauer to murder all the leaders of NK, alone with eyes closed.