With Russia and Ukraine at war, the situation in Northeast Asia is heating up. North Korea’s Kim Jong-un has launched a dozen missiles so far this year, including one long-range vehicle thought to include components of an ICBM capable of hitting America. Worse, Pyongyang suggested it is prepared to restart ICBM and nuclear tests.

Earlier this month, South Korean voters narrowly elected a hawkish conservative, Yoon Suk-yeol, to replace outgoing progressive President Moon Jae-in. Yoon promised to take a tougher position toward the North, which likely will turn the bilateral relationship actively hostile.

Kim appears to lack interest in engaging with the U.S. After his February 2019 summit with President Donald Trump collapsed, Kim largely ended contact with Washington, ignoring multiple offers from the Biden administration to talk.

In the past, Kim used missile tests to push Washington to negotiate and make concessions. Before returning to diplomacy, he may have decided to bolster his arsenal. At various party gatherings and military parades, Kim has presented lengthy weapons wish lists. Despite his country’s evident economic weakness, Kim’s government has made significant progress on several new weapons systems. The Rand Corporation and Asan Institute provide this ominous assessment:

[B]y 2027, North Korea could have 200 nuclear weapons and several dozen intercontinental ballistic missiles (ICBMs) and hundreds of theater missiles for delivering the nuclear weapons. The ROK and the United States are not prepared, and do not plan to be prepared, to deal with the coercive and warfighting leverage that these weapons would give North Korea.

In that case, the Democratic People’s Republic of Korea would possess an arsenal comparable to those of the world’s second-tier nuclear powers. That would give Kim room to move, offering some weapons in exchange for sanctions relief while retaining enough nukes to deter a U.S. attack. Imagine if the DPRK had 100 weapons and missiles capable of targeting the American homeland. Any U.S. president would hesitate to intervene even in a conventional war on the Korean Peninsula, since North Korea could threaten to shoot unless Washington backed down.

South Koreans have grown more uncomfortable as Pyongyang has developed its nuclear-weapon and missile capacities, though the South Koreans might intuitively understand the limits of extended deterrence. In any case, people in South Korean increasingly want the ability to protect themselves without having to rely on a sometimes-mercurial and even feckless Uncle Sam. After all, if pressed to risk Los Angeles for Seoul, most Americas would naturally say, “No thanks.”

For at least a decade, a majority of South Koreans have favored developing their own nuclear deterrent. Although a plurality still identify the DPRK as the likeliest villain, an increasing number now cite the People’s Republic of China as the greatest future threat to South Korea. More than half of those surveyed figure the PRC will become the most serious danger to South Korea in the coming decade.

The most impressive poll number on this point is a 2021 poll by the Korea Institute for National Unification, which found 71.3 percent of respondents backed acquiring nukes if the North did not abandon its program. And 61.6 percent of those surveyed wanted to keep nuclear weapons even after reunification “as a means of securing sovereignty and survival rights from neighboring powers.” A 2020 Asan Institute survey found 69.3 percent of respondents favored developing an ROK bomb in response to North Korea’s program.

Last month, the Chicago Council for Global Affairs published a detailed study of South Korean support for nuclear armament, finding 71 percent of surveyed South Koreans wanted the country to possess its own nuclear deterrent. The Chicago Council found that “When asked to choose between the two, the public overwhelmingly prefers a domestic weapons program to deployment of [U.S.] nuclear weapons,” adding that “support for both options appears to be insensitive to potential negative repercussions for South Korea’s relations with China, South Korea’s economic security, the alliance with the United States, or hopes for North Korea’s denuclearization.”

The Council found that South Koreans want the bomb even though they believe the U.S. would still protect the South in the event of war, noting that “Confidence that the United States will carry through on alliance commitments is positively associated with support for nuclear weapons, contrary to beliefs that alliance commitment concerns are a main driver of public views on nuclear acquisition.”

Notably, respondents had an overwhelming preference (67 percent to 9 percent) for the South’s own nukes over a return of American tactical nuclear weapons. President-elect Yoon favors the latter. However, so-called extended deterrence is becoming untenable. When the DPRK was only a conventional power, it posed a military threat to the Republic of Korea alone. Extended deterrence was a freebie, allowing Washington to threaten the use of nukes in even a conventional contest. The North’s main deterrent at the time was its conventional threat, especially with artillery and missiles, against the Seoul metropolitan area.

However, as Pyongyang has acquired nuclear weapons and developed ICBMs, the U.S. faces a future in which the DPRK could strike back against the American homeland. Although Washington retains overwhelming military and nuclear strength, North Korea will eventually be able to target U.S. possessions and military bases in the Asia-Pacific, Hawaii, and several mainland cities.

The ROK is a good friend, but the relationship is not worth bringing mass destruction and death to America. The U.S. might even have to reconsider the alliance if Washington were to intervene in a conventional fight on the peninsula that it could not afford to win, lest North Korea use its arsenal, or threaten to do so. Although Kim Jong-un has given no indication that he wants to leave this world atop a radioactive funeral pyre in Pyongyang, he might prefer that to more mundane defeat.

Of course, Washington’s attitude would be critical if Seoul decided to take the nuclear path. In the 1970s, President Park Chung-hee cancelled the ROK’s nuclear program when confronted by the Nixon administration. Having since failed to stop the North’s progress, the U.S. would have little credibility today were it to inveigh against a similar South Korean effort. Washington will likely be reluctant to sanction one of its closest military allies, which it views as playing an important role in constraining China.

Indeed, Beijing’s growing strength suggests Washington should rethink its stance on nuclear proliferation. America’s unusual dominance upon exiting World War II allowed it to play global policeman, at least in regions it cared about. However, that moment is gone. In an increasingly multi-polar world in which the U.S. faces grave economic and military challenges, it cannot afford to continue providing nuclear guarantees to all of its allies.

Moreover, America’s current weapons policy is a bit like domestic gun-control policies—it is most effective in denying weapons to friendly, responsible parties. In the case of nuclear weapons, that means America keeps nukes from democratic, allied states even as bad regimes arm themselves. Forget Iran: Pakistan already has put nukes in the hands of a dangerously unstable state beset by Islamist extremists. India, with its increasingly authoritarian Hindu-nationalist regime, has created a countervailing force. North Korea, too, is a growing nuclear state, despite Washington’s refusal to acknowledge the obvious.

Even before the Russian attack on Ukraine, both Japan and South Korea were increasing military outlays. Given both nations’ concerns about China and DPRK, they should be doing even more than they are. However, the most important constraint on Chinese adventurism would be allowing Tokyo and Seoul to possess small but survivable deterrents.

To be sure, there are downsides to nuclear proliferation. However, Ukrainians noted that if they had used leftover Soviet weapons for their own nuclear program, Moscow would not have invaded. Rather than putting America’s homeland on the line for countries with whom we are friendly but are not vital for U.S. security, allowing them to acquire nuclear weapons would provide them a direct means of defense.

If North Korea forges ahead to create a sizable nuclear arsenal, Washington will have to decide whether it is willing to risk national destruction to continue protecting the ROK. If not, then Washington should contemplate the currently unthinkable—a South Korean nuclear weapon. The South Korean people appear ready to shoulder that responsibility. How would U.S. policymakers respond?