How bad would a nuclear-armed South Korea be? Let us count the ways.

Earlier this month, South Korea tested a ballistic missile from a submarine, making it the only country without nuclear weapons to do so. The test followed US-South Korea discussions about the possibility of collaboration on proposed nuclear-powered submarines—a move that could provide South Korea fissile fuel stockpiles not subject to inspections by the International Atomic Energy Agency (IAEA). South Korea’s interest in these dual-use military technologies suggests support for an independent nuclear arsenal is no longer only on the fringes. The South Korean public has, for years, largely supported proliferation, in part out of concern about relying on the US nuclear security guarantee. Numerous South Korean political leaders, including the leading conservative party presidential candidate, Hong Joon-pyo, have been outspoken about South Korea’s need “to independently seek nuclear armament.” Even some US academics claim South Korean nuclear proliferation “might be the best course” for Seoul, arguing the United States should “render political support” if South Korea chose to proliferate.

These expressions of support notwithstanding, a South Korean effort to obtain nuclear weapons would be costly, and it would endanger South Korea’s geopolitical situation. Nuclear weapons would hardly improve South Korea’s ability to deter North Korea and China. And rather than support a nuclear South Korea, the United States would be better off investing in nonnuclear solutions to East Asian security challenges.

In the first place, South Korea’s existing efforts to manage relations with both the United States and China are working. South Korea has affirmed support for the ‘Quad’—a security partnership among Australia, India, Japan, and the United States—without officially joining. Under President Moon Jae-in’s “New Southern Policy,” South Korea has built much stronger economic and diplomatic ties in Southeast Asia and India. South Korea has expanded regional security cooperation as well, with improved coordination on issues like law enforcement and cybersecurity and with the implementation of joint military exercises aimed at peacetime activities like search and rescue. This approach allows South Korea to balance against China without direct confrontation. South Korea and China cooperate on core issues like trade, North Korean denuclearization, and pandemic management.

South Korea’s relations with North Korea also show signs of warming. The cross-border “hotline” between North and South Korean leaders was recently reopened, with officials from both states holding their first phone call in several months. North Korea has also reached south to suggest its willingness to hold diplomatic talks. North Korea has been badly hit by the coronavirus, natural disasters, and ongoing sanctions, so the time may be right for a resumption of negotiations. The situation, though, remains delicate. Should South Korea take steps towards a nuclear weapons capability, diplomacy would be radically altered.

If South Korea nevertheless concludes it needs nuclear weapons, it will find them costly and dangerous. Unless South Korean withdrawal from the Non-Proliferation Treaty (NPT) was seen as as occurring in “good faith,” the UN Security Council could levy punishment. China, at least, would push hard for this outcome. South Korea could also face blowback from the United States. Nuclear proliferation would violate the commitments to peaceful, civilian usage of nuclear infrastructure included in the US-South Korea nuclear cooperation agreement. Violations would give the United States the right to demand the return of any transferred nuclear technologies or materials. It could also enable sanctions. While the United States may face some political difficulties levying sanctions on a proliferating ally, it has happened before—for example, with Pakistan and South Africa.

Moreover, China and North Korea would be loath to quietly accept a South Korean nuclear arsenal. China’s dismayed reaction to the deployment of the Terminal High Altitude Area Defense (THAAD) missile defense system illustrates how seriously it takes threats to nuclear deterrence. Meanwhile, North Korea has consistently called out perceived challenges to its nuclear security, including South Korean missile developments and joint US-South Korean military exercises, and has repeatedly demonstrated willingness to escalate in response. Pyongyang would likely do whatever it could to undermine South Korean resolve if Seoul expressed serious interest in building nuclear weapons.

Neither would nuclear weapons necessarily be useful for deterring China and North Korea. Nuclear-armed adversaries are no less prone to wars and do engage in lower-level belligerence. For example, China has continuously engaged in territorial contests with India. Beijing’s ongoing nuclear buildup also suggests a shift in the military’s strategic thinking that may privilege nuclear weapons. Meanwhile, even the United States has had limited success leveraging nuclear assets to deter North Korea.

South Korea should pursue a non-nuclear solution to its security problems. Ongoing efforts to develop an effective “conventional counterforce” strategy, which would leverage conventional military assets to deter nuclear threats, could be an important part of this equation. South Korea should also continue to pursue talks with North Korea, invest in regional initiatives (without explicitly counterbalancing China), and encourage the United States to engage China on arms control.

Fortunately, the Biden administration can make this process easier. The White House has several openings to both reinvigorate nonproliferation and reduce the threats South Korea faces. The Nuclear Posture Review (NPR) offers an opportunity to reiterate alliance commitments and reduce the role of nuclear weapons. The upcoming NPT Review Conference represents a chance to reinvigorate nonproliferation norms and reopen conversations about arms control. This could set the stage for the White House to fulfill its promises to “pursue arms control to reduce the dangers from China’s modern and growing nuclear arsenal,” as well as to restart talks with North Korea. Continued diplomacy will also play a crucial role in navigating better ways to support South Korea. These efforts won’t be easy, although they would be helped by a fuller staff of qualified diplomats. But done effectively, they could help preserve nuclear nonproliferation and produce better strategic stability.

Editor’s note: The first sentence of this article has been corrected to clarify that the ballistic missile test was from a submarine and that there was only one missile.