We don't need nukes to deter China (or any other country) from an all-out invasion. We already deter them by being a small, heavily populated and industrially

We don't need nukes to deter China (or any other country) from an all-out invasion. We already deter them by being a small, heavily populated and industrially developed, largely monocultural, and largely mountainous country, which has half a million soldiers and is only accessible via sea or through one of the world's most heavily fortified border. Invading South Korea will cost any country more than Invading Iraq cost America. It's simply not worth it. That's not saying South Korea is invincible, or there aren't any ways China can apply military pressure. A much more realistic scenario is like this: some Chinese patrol ships suddenly find a need to "protect" Chinese fishing boats from being "harassed" by South Korean coast guards patrolling its EEZ. In such a case, nukes won't help, because what are you going to do with them, bomb Beijing? Can you imagine what would happen to KOSPI index if a South Korean politician so much as made a joke about using nukes? I still fail to see the utility of nukes. Any national leader has to be batshit insane to consider invading South Korea, and if they are already that insane, I don't see how having a few nukes will suddenly cause them to back down. (Don't be fooled by North Korea: they're carefully cultivating the image of a batshit insane trigger-happy country because it benefits them.)