South Korean President Yoon Suk Yeol is accelerating a once unthinkable debate over whether his country should acquire nuclear weapons — a move that would transform the U.S.-South Korea alliance and upend regional security dynamics.
Last week, Yoon made global headlines when he suggested during a policy briefing that South Korea could get its own nuclear arms if the security situation with North Korea worsens.
Yoon’s comment was delivered in an almost off-handed manner and framed as part of a worst-case scenario; his aides quickly claimed South Korea was not backing away from its commitments under the nuclear Non-Proliferation Treaty.
Nonetheless, Yoon’s comment was unprecedented, at least for the period since South Korea became a democracy.
“It’s a very important development,” said Cheong Seong-chang, a senior researcher at the Sejong Institute, a nonpartisan foreign policy research organization outside Seoul. “Until now, the South Korean government had never considered independent nuclear armament, even as a ‘plan B.’”
For Yoon, talking about nukes has become a pattern.
As a presidential hopeful in late 2021, Yoon said he would consider asking for the redeployment of U.S. tactical nuclear weapons that were removed in the early 1990s. He also recently said the United States and South Korea were discussing nuclear cooperation, which he envisioned would eventually have the same effect as NATO-style “nuclear sharing.”
Yoon’s motives, in some ways, are straightforward.
North Korea recently has engaged in more frequent threatening behavior while rapidly expanding its nuclear arsenal. In comments published on New Year’s Day, North Korean leader Kim Jong Un vowed to “exponentially” increase his stockpile of nuclear warheads.
Many in Seoul believe current U.S.-South Korea alliance structures need to be strengthened in order to compensate for North Korea’s growing threats. As part of those efforts, they want bigger displays of allied military strength, including with U.S. nuclear assets.
On a broader level, there are also concerns about the durability of Washington’s defense commitment to South Korea, especially given recent U.S. political turmoil and the relative popularity of so-called “America First” foreign policy ideas.
Those dynamics help explain the growing wave of scholars, former officials, and ex-officials who now publicly support South Korea developing its own nuclear weapons.
What Yoon wants
Analysts are divided, though, over what Yoon intends to accomplish with his nuclear weapons talk. Few believe South Korea would actually pursue nuclear arms, at least anytime soon, given the massive economic and security risks that would accompany such a move.
Instead, Yoon could be using the issue to send a tough message to North Korea, or to satisfy his conservative allies who support a more aggressive approach toward Pyongyang.
Some former senior South Korean military officials have called for South Korea, already a major producer of nuclear energy, to enhance its ability to acquire nuclear weapons, if it chooses to do so. Yoon’s comments may be designed to eventually make that idea more palatable, some analysts note.
But the most obvious explanation is that Yoon wants to publicly pressure the United States to provide more robust defense assurances, according to Go Myung-hyun, a research fellow at Seoul’s Asan Institute for Policy Studies.
“I think Yoon wants the Biden administration to offer further strengthening measures for extended deterrence,” Go said. “He wants to highlight how seriously he views the North Korean threat.”
In recent months, South Korea and the United States have agreed to increase joint military drills and more frequently deploy nuclear-capable U.S. bombers and aircraft carriers to the region. Last week, South Korea’s military announced it would hold a “table-top” exercise with the United States that would include the scenario of North Korea using a nuclear weapon, though U.S. officials said the idea of "joint nuclear exercises" is off the table.
For some in Seoul, those steps are inadequate. South Korea, they argue, should have a bigger role in the planning and execution of U.S. nuclear forces. But South Korea may never be fully satisfied, since the U.S. president is the ultimate decider of whether U.S. nuclear weapons are used in any individual scenario
What is next?
While Yoon may think that publicly raising the nuclear option will force the United States to provide more security guarantees, “it is likely to have the opposite effect of straining the relationship,” according to Eric Brewer, a former White House National Security Council official.
Brewer, now at the Washington DC-based Nuclear Threat Initiative, said the United States “should balance firmly closing the door on any further talk of South Korea weaponization while avoiding a public spat with an ally.”
“The U.S. should be clear in public that it would not support South Korea’s acquisition of nuclear weapons and that Washington and Seoul are both focused on the real, and ongoing joint efforts to strengthen the alliance. It should also reinforce privately that such comments about developing nuclear weapons are counterproductive both to dealing with the North Korea threat, as well as efforts to enhance U.S.-ROK security cooperation and extended deterrence,” he added.
If Seoul were to pursue nuclear weapons, it could risk breaking the U.S.-South Korea alliance, Brewer said.
“The idea that, if South Korea can just convince the United States to allow it to go nuclear, everything will be ok is fundamentally misguided. It would still risk Congressionally required sanctions, a de facto end to international cooperation for its civil nuclear energy program, and a severe response from China,” he added.
But if North Korea continues its provocative missile launches and other weapons tests, Yoon will keep feeling pressure to do more, said Go of the Asan Institute.
“There are two ways things can get worse for South Korea. One, the North Korea threat gets worse, say with an exponential increase in nuclear stockpile and ICBMs,” he said. “Two, is somehow the U.S. response strategy stays inadequate.”
Lee Juhyun contributed to this report.