South Korea would gain an appealing symmetry with the North through nuclear weapons—but likely would never use them.

It was probably inevitable that South Korea would entertain the development of nuclear weapons in the face of North Korea’s relentless push for them itself. That conversation is now increasingly widespread on TV and in the media here. Unsurprisingly, conservatives are calling for it; they have for awhile. Butother, more moderate voices are kicking it around too, and television pundit shows are filled with this now. An alternative to this is the demand to bring American tactical nuclear weapons back to South Korea. A debate that has been on the fringe of South Korean political life for decades is now having its most robust public discussion ever. For the first time, a clear majority of South Koreans want this capability.

Nuclear weapons are appealing for obvious reasons. They offer an attractive symmetry with now-nuclear North Korea. Nuclear weapons signal global prestige to others, as well as a seriousness and weight in international relations. On the peninsula, they might create a more robust perception of mutually assured destruction (MAD) between South and North Korea. MAD is the notion that two hostile nuclear powers can nonetheless live in a cold peace, because they mutually deter one another with the threat of massive retaliation. South Korea already enjoys MAD in a sense because of the American nuclear umbrella. The United States extends nuclear deterrence to the South. It threatens to strike North Korea with nuclear weapons if North Korea were to do so to South Korea.

But this ‘borrows’ American nuclear weapons, rather than placing them directly under the command of the South Korean president. Despite the tightness of the U.S.-South Korean alliance, local control of such powerful weapons will always be deeply attractive to any sovereign state. And now that North Korea might be able to strike U.S. cities with nuclear weapons, there is a burgeoning debate over whether the United States will ‘risk San Francisco for Seoul.’ That is, if North Korea were to attack South Korea and simultaneously threaten the United States with nuclear attack if it joined the war, would the United States, in fact, join? Much the same debate took place throughout the Cold War. After the Soviets ranged the continental United States with missiles, the European allies became anxious enough about America’s commitment that two of them—Great Britain and France—went nuclear themselves. This same logic appears to be playing out in South Korea, and possibly Japan.

So far, the South Korean liberal administration has rejected this effort, and the U.S. government too has been cool to either proposal—indigenous South Korean nuclearization, or the return of U.S. small nukes to the peninsula. Both sides fear that Southern nukes would just add to the panic and help justify the North’s program and Chinese foot-dragging about it. But there is another important reason why South Korea does not need nuclear weapons: South Korea is unlikely to ever use them against North Korea, even it is nuked by it.

In a scenario so extreme that Seoul was seriously considering nuking North Korea, South and North Korea would be on the verge of, if not already in, a final death struggle to control the peninsula. That is, they would already likely be at war before South Korea even considered such a dramatic option. But in a final war between North and South, South Korea (and the United States) would imminently invade North Korea, which would in turn make South Korea responsible for the blast zones and chaos nuking North Korea had just created. South Korea’s wartime goal of destroying and absorbing North Korea—especially, ironically, if North Korea had nuked South Korea—makes it a bad idea to counter-nuke the North because occupation, including inheriting North blast zones, would happen shortly afterward.

This is an important distinction between the Korean case of nuclear deterrence and others, such as the United States and the Soviet Union/Russia, the United States and China, or India and Pakistan. In each of those cases, neither side wants to absorb the other. This makes the use of nuclear weapons less costly to the side who launches. In the Cold War case, the United States and Soviets would have cared little for the cleanup of the destruction they wrought on the other. The primary burden of rebuilding would have fallen the side struck.

That is not so in Korea. South Korea has, de jure at least, revisionist aims regarding North Korea. It wishes to eliminate North Korea, absorb its territory and people, and govern it. This is even written into the South Korean constitution. This generates curious effects regarding threats of extreme force. If South Korea were in a situation of considering nuclear force against North Korea, that situation would be so extreme that South Korea would probably be invading and destroying North Korea. If South Korea were to do that, it would then inherit the nuclear destruction it had just wrought. This creates the inverted incentive not to nuke North Korea even if North nukes South Korea first. So long as South Korea could still win a conflict with North Korea, nuking North Korea would dramatically worsen the South’s postvictory obligations and costs. Better for a unified Republic of Korea to begin with blast zones in only one portion of the country, not both.

The only scenario then in which South Korea might counter-nuke North Korea is if North Korea were actually winning a war against the South. If that were the case, the South might use battlefield nuclear weapons to slow the North’s progress, just as NATO considered such weapons to slow a Red Army advance on the West. But so long as South Korea could reasonably envisage winning the war—which it most definitely would do as long as its alliance with the United States holds—Seoul is in the curious position of not using nuclear weapons under almost any circumstances, because it would shortly be responsible for the cleanup of that use.

In short, not only would South Korean nuclear weapons unnerve the region, South Korea would likely not use nuclear weapons even if the North did. The case for Southern nuclearization is, in fact, curiously weak, despite the appearance of symmetry and appearance keeping up with the North.