As for the Koreas - I read a study that said the North has between 15,000 to 18,000 artillery pieces aimed at the South, and that it is this threat towards Seoul that is the real problem even when compared to the budding nuclear issue. Many of these artillery pieces are just over 18 miles away from Seoul. By the time enough of those artillery pieces were removed from the equation the city of Seoul would be a sea of fire, and there is still no way to negate that artillery quickly (unless one considers a heavy nuclear attack all across the artillery locations - which is obviously something that is beyond the call of any American president, Democrat or Republican, for the last 2 decades). Without the threat of the artillery barrage I believe the South would be able to smite the North pretty hard ...they have an overwhelming qualitative advantage in the air (e.g. one of the most advanced F-15 variants, the F-15K), in the sea (one of the most potent AEGIS destroyers, and the most heavily armed, in the world, the Sejong the Great class), on land (they have one of the most powerful Main Battle Tanks in the world, with the K1A1 that is a variant of the Abrams tank, and the K2 which is said to not only be the most expensive tank in the world but arguably the best once its development is finalized). They have armed forces that know their job, and thus in a war could give the North Koreans a truly tough time.
However, there are still those artillery pieces.
Until they are taken care of there will be no way the South will retaliate against the North under any circumstances apart from a full-on full-scale assault. This means, in my opinion, the only time the South will retaliate against the North is if the North actually goes ahead and uses the artillery against Seoul. It is sort of like one of those circular loops in Excel ...the South will not attack because of the artillery, and the only time the South would attack is if the artillery is used in a big scale against them.
Until then, Pyongyang can order South Korean ships (like the Cheonan) to be sunk ...with no response. Pyongyang can order South Korean towns to be shelled (like what happened when a small SK town was shelled some time back) ...no response. Until there is a way to neutralize that artillery, Pyongyang can do (almost) anything to Seoul, apart from a massive attack, and nothing will happen. As long as that artillery
As long as that artillery is in the picture their hands are tied.
Artillery piece meets Hellfire Missile launched from Apache Attack helicopter— no more artillery piece. Hungry North Koreans say ‘’To Hell with Dear leaders kid, I’m outta here.’’ I truly think neither Korea wants a repeat of 1950.