South Korean nuclearization has become a live issue in the political and policy debate in Seoul and in Washington. The continued expansion of North Korea’s nuclear arsenal and unsuccessful U.S. efforts to coerce North Korean disarmament have convinced a large majority of South Koreans that nuclear armament is desirable for their country.

 According to a study by the Asan Institute for Policy Studies, 69 percent of the public in South Korea supports the acquisition of nuclear weapons. That represents a significant increase from 55 percent in 2010. Members of the conservative People Power Party opposition have seized on this issue. Presidential candidate Yoon Seok-youl has called for the U.S. to redeploy tactical nuclear weapons to the peninsula. 

Another, Yoo Seong-min, pledged to seek a nuclear sharing agreement with the U.S. if elected. Another leading candidate, Hong Joon-pyo, has expressed support for nuclear sharing between the U.S. and South Korea and the possible development of South Korea’s own weapons program. “Nukes can only be countered with nukes,” Hong told Bloomberg News in an interview last month. Some experts in the United States agree. Jennifer Lind and Darryl Press recently made the case that the best way forward for shoring up the U.S.-ROK alliance is to support South Korea’s acquisition of nuclear weapons. 

Given that North Korean disarmament is extremely unlikely under any circumstances, there is a certain logic to the idea that South Korea should be able to have its own deterrent as well. But there are several pitfalls that should give both the U.S. and South Korean governments serious doubts about opening the door to more proliferation. 

South Korean nuclearization would send a signal to other states that the U.S. no longer takes nonproliferation seriously by proving beyond any doubt that it insists on nonproliferation only for its adversaries and not for its allies. It would almost certainly lead to other allies building their own nuclear weapons. Even if others didn’t immediately follow South Korea’s example, Seoul’s acquisition of nuclear weapons would further fuel an arms race in East Asia, and heightened tensions with both China and North Korea are bound up with that. Finally, it would make any crisis in the region that much more perilous by introducing at least one more nuclear weapons state into the mix. 

While South Korean interest in having their own deterrent is understandable, more proliferation is not the answer to the threat posed by North Korea’s arsenal. “In terms of South Korea’s security, nuclear weapons do very little,” arms control expert Jeffrey Lewis told Foreign Policy last month.

Lauren Sukin and Toby Dalton have answered Lind and Press’ argument, and they contend that “South Korean nuclear acquisition would be counterproductive and dangerous, leaving both the alliance and South Korean security worse off.” They argue that the alliance is strong enough that South Korean nuclear weapons are not needed to bolster it, and that a South Korean nuclear weapons program could invite more coercive Chinese behavior in the form of economic boycotts and shows of military force. If China punished South Korea severely for hosting a missile defense system, how much worse would their reaction be to South Korean nuclear weapons? 

If the security implications for South Korea are troubling, the effects of South Korean nuclearization on the global nonproliferation regime might be even more harmful. Almost all states around the world belong to and abide by the Nuclear Non-Proliferation Treaty (NPT), and the NPT has been a great success for the most part in preventing the spread of nuclear weapons. If South Korea were to pull out of the treaty with Washington’s blessing so that it could build its own nuclear arsenal, that would significantly undermine the treaty and encourage others to follow South Korea’s example. Japan would likely be the first to follow, but it would not be the last. This would not be the boon for regional security that many assume. As Euan Graham observed a few years ago, “At best, it is an expensive chimera; at worst, it will strike at the foundations of peace.”

There is a plausible alternative of seeking an arms control agreement with North Korea that could put limits on the size and deployment of their arsenal. This would not eliminate the threat, but it would go a long way towards managing and stabilizing the situation. Negotiating such an agreement becomes much less likely if South Korea becomes a nuclear weapons state. Few things would be more likely to intensify North Korean insecurity than South Korea’s acquisition of nuclear weapons. Since North Korea consistently responds to pressure with its own pressure tactics, a nuclear-armed South Korea would likely be facing more aggressive behavior from its neighbor rather than less.

Acquiescing in South Korean nuclearization or actively encouraging it would not be in the American interest, and it would serve U.S. strategy in the rest of Asia poorly. As Van Jackson explained in a recent article for Foreign Affairs, the U.S. has already been making the mistake of having a “military-first” approach to Asia. Giving a South Korean nuclear arsenal the U.S. stamp of approval would compound that error. As it is, the U.S. is already encouraging arms buildups in the region. The AUKUS partnership announced earlier this year already raised some serious concerns in Southeast Asia about the destabilizing effects of intensified rivalry. Imagine how much more alarming the addition of a new nuclear weapons state would seem to other countries in the region. 

Responsible alliance management sometimes means opposing a dangerous course of action that an ally wishes to take. This may create short-term strains in the relationship, but it can prevent an ally from making a costly blunder. If the alliance with South Korea needs strengthening, there are other and better ways of reassuring them of U.S. commitment than giving a green light to acquiring nuclear weapons.

For one thing, the U.S. could waive sanctions that have been blocking economic cooperation with North Korea. This is something that the current South Korean government has been wanting, and it would also help to reduce tensions on the peninsula. As the former commander of U.S. Forces Korea, Vincent Brooks, has said, nuclear weapons do not give South Korea an advantage. In fact, he warned, they could prove to be a liability if they escalate tensions with North Korea unnecessarily. The best argument against South Korean nuclearization is that South Korea does not need to have nuclear weapons to remain secure and acquiring these weapons will bring new risks and costs that could be avoided.

The decision to acquire nuclear weapons is ultimately one for the people of South Korea to make, but it is incumbent on the United States as an ally to warn them of the potential dangers and costs that could come with choosing that path.