I've read that a new Korean War could kill millions. But unless it goes nuclear--and by definition a preemptive strike campaign in this context takes place before North Korea has nuclear weapons--that is a gross exaggeration.
Yes, a large number of South Koreans are in and near Seoul, which is close to the DMZ.
But they do have shelters.
And only a small number of the North Korean artillery pieces can hit Seoul from where it is. To really use a lot of that artillery it has to go into the open and advance south behind a North Korean army push across the DMZ.
And I don't think the North Korean army can pull that advance off; nor do I think the North Korean artillery could survive for long moving and deploying in the open.
Nor do I think Russia is capable of resupplying the North Korean armed forces to allow them to sustain a war; nor do I think China would sustain a North Korean offensive as long as we don't try to conquer North Korea.
I know North Korea has nuclear devices. Do they really already have nuclear weapons? The consensus says they do not. Are we wrong?
That's the key question. If America failed to strike while North Korea had no nuclear weapons, we really might be too late to attack. Shame on the American president who let that happen on their watch.
And if we weren't able to determine this nuclear status, what the Hell was all the talk over the last 15 years from the Left that we should only take action when a country's crossing of the nuclear threshold is imminent? I never believed we could detect such a status with enough precision to make it meaningful. But what do I know? I'm a Neanderthal.
Did we really miss the "imminent" window for justifiable action?
If North Korea does not yet have nuclear weapons, the cost of a strike campaign will be far less than the worst case by multiple orders of magnitude.
If North Korea does have deliverable nuclear weapons, the risk for more casualties goes up. Then the question is whether our nuclear weapons deter North Korea from using their nukes in response to an attack campaign that does not seek regime change in North Korea. Would North Korea commit suicide by striking out with nukes? Because we would nuke North Korea if that happens.