South Korea is not our problem. They have had half a century to prepare for this and instead built cell phones and cars...using our money and military.
They better prepare now.
Trump and everyone who is everyone that matters says otherwise. It is big of you not to care about millions of souls, but decent and humane people do. Why should they provide defense for themselves when we have done that for 50 years. To dump them now is criminal. Whether we should have provided defense for the last 50 years is worthy of debate, but it is too late to change now - on a dime and say never mind - that is rather cowardly. We have provided SK cover and because of that it is not possible to turn them lose at this moment. That process should have started years ago, but it is too late to pretend they should be on their own.
Our own DoD and others estimate millions of SK would probably be killed if we attacked NK. We will not be able to intercept all their missiles or hold back their army. NK has over a million troops, thousands and thousands of tanks and nearly 1,000 aircraft. NK would be able to overwhelm SK quickly bringing with them killing fields that would be mind blowing.
It is rather cowardly to state you don't care about SK - that is selfish and evil to the extreme.
This doesn't even include what retaliation China would bring on us and SK.
The US gave NK the money to build their nukes (it was in the 90s and Bill Clinton did it) which is another reason why we are in this mess and it is our mess - we caused it by appeasing them.
The only sane thing is too work through China. We both need each other, but China needs us more than we need them.