Stronger Alliance or Nuclear Weapons? North Korea’s Military Might Means Tough Choices for South Korea

Summary: North Korea's recent escalation in rhetoric, declaring South Korea as its "principal enemy," may not signal an imminent military threat but does indicate a strategic shift with significant implications for regional stability. This change comes as North Korea's advancing nuclear capabilities, including ICBMs that can reach the U.S., complicate the strategic calculus for South Korea and its allies.

North Korea's Harsh Rhetoric Shifts Regional Power Dynamics

In January of this year, Pyongyang’s language towards South Korea took on a new and much more bellicose tone. North Korea’s leader, Kim Jong-un, described the South as his country’s “principal enemy,” and announced that its citizens should no longer be regarded as “fellow countrymen,” foreshadowing the removal of the commitment to reunification from North Korea’s constitution. Some highly respected analysts have argued that this rhetorical shift indicates a sharply increased risk of North Korean military aggression across the DMZ. Others argue that nothing has really changed and that the new rhetoric simply reflects political maneuverings within North Korea rather than a substantial change in the threat it poses to the South. 

I’d like to suggest a third interpretation: while the risk of a large-scale North Korean military assault on the South remains very low, Pyongyang’s newly hostile tone portends a very significant shift in the strategic balance on the Korean Peninsula, with important implications for America’s position in East Asia more broadly.

This interpretation reflects the profound but often underestimated consequences of North Korea’s growing nuclear and missile capabilities for the strategic situation in the Western Pacific. In recent years, Washington’s attention has shifted away from the North Korean problem, but it has not gone away. Pyongyang is now believed to have at least twenty nuclear weapons and perhaps the material to build seventy. It has also developed a range of increasingly sophisticated ballistic missiles to deliver them, including intercontinental-range ballistic missiles (ICBMs) that can reach the United States itself.

North Korea’s ICBMs fundamentally change the strategic calculations of all the key players and immensely increase the significance of North Korea’s nuclear arsenal. That is not because Pyongyang might mount an unprovoked nuclear attack on America itself—the certainty of massive U.S. retaliation makes sure of that. But it intensifies North Korean nuclear threats to U.S. allies by undermining the credibility of extended deterrence. Hitherto, it has been relatively easy for America to neutralize Pyongyang’s nuclear threat to South Korea and Japan. Its promises to mount devastating nuclear strikes on North Korea in retaliation for any North Korean nuclear attacks on U.S. allies or partners have been highly credible as long as North Korea could not hit America back.

Now, Pyongyang can respond to a U.S. retaliatory attack on North Korea with a counter-retaliatory nuclear strike on the United States. Washington would try to minimize this threat with preemptive strikes on North Korea’s ICBMs, but big risks would remain. The potential cost to America of fulfilling its extended deterrence promises to its allies is, therefore, much higher than it was before, so the risks of America reneging on them in a crisis are much higher, too.

That has enormous implications for strategic calculations in Seoul, Tokyo, and Pyongyang. Let’s start with Seoul. Pyongyang’s ability to strike the United States will radically undermine Seoul’s confidence in U.S. extended nuclear deterrence. South Korean decision-makers must now recognize the real danger that the North Koreans will convince themselves that they can launch a nuclear attack on South Korea without incurring a U.S. retaliatory strike on themselves because they believe that the threat of North Korean counter-retaliation against the United States itself would deter Washington.

This confronts Seoul with a real problem. The danger is not so much that Pyongyang would actually launch a nuclear attack on the South. It is that North Korea could use the threat of nuclear attack to compel the South to do its bidding. The more uncertain a U.S. retaliatory response becomes, the more credible a North Korean threat of this kind would be, and the more likely it becomes that Seoul would have no choice but to comply with whatever demands Pyongyang might make. Moreover, the harsh new tone of Pyongyang’s rhetoric towards the South makes it seem less unlikely that the North might try to use nuclear blackmail this way. By repudiating the idea of peaceful reunification and instead declaring South Korea to be an enemy that must be subdued by force, Kim Jong-un might be setting the scene for just this kind of confrontation.

What can Seoul do in the face of this new and grave danger? It has only two options. One is to try to strengthen the credibility of U.S. extended deterrence. The other is to cease depending on Washington and instead build its own nuclear forces to counter and neutralize North Korean nuclear threats. The second option must be taken very seriously. In January last year, President Yoon openly canvassed the idea that South Korea might need to build its own nuclear weapons to counter North Korea’s. Polling suggests that 60 to 70 percent of South Koreans would support this move. South Korea is well-placed technically to develop nuclear weapons and has already built ballistic-missile firing submarines to deliver them. 

Although President Yoon quickly stepped back from his comments, Washington plainly took them seriously. A few months after he made them, Yoon was invited to the White House, where he and President Biden issued the “Washington Declaration,” in which ringing reaffirmations of America’s extended-deterrence commitment to defend South Korea were matched by equally plangent affirmations South Korea’s confidence in U.S. commitments and promises not to develop its own nuclear forces. The declaration announced new forums for closer consultation between Washington and Seoul on nuclear questions, including the establishment of a Nuclear Consultative Group modeled on NATO’s Nuclear Planning Group, and contained a U.S. promise to “further enhance the regular visibility of strategic assets to the Korean Peninsula” by more frequent visits by nuclear-capable U.S. forces.

However, the Biden Administration stopped short of taking two steps that would have more materially addressed Seoul’s concerns. It did not agree to the kind of “nuclear-sharing” arrangements that exist between the United States and some NATO allies. Nor did it agree to redeploy nuclear weapons to South Korea, which again contrasts with its continued basing of nuclear weapons in Europe. It seems Seoul asked for both, and Washington declined. It is worth reflecting on this.

In the face of the growing uncertainties about America’s resolve created by Pyongyang’s growing ICBM capability, Washington has refused to offer Seoul the same mechanisms of reassurance that it extended to its European allies since the Cold War. That is hardly reassuring. Indeed, it risks the Washington Declaration having an effect that is opposite to that intended. By setting such clear limits on what America is willing to do, it weakens rather than strengthens South Korean confidence in U.S. resolve. So, it is hardly surprising that the Washington Declaration has not assuaged South Korean concerns about the credibility of U.S. extended deterrence.

So what should the Biden Administration do instead? What would be required to fully convince both Seoul and Pyongyang of America’s resolve to defend South Korea, even at the risk of North Korean nuclear attacks on U.S. cities? When thinking about this, it is worth looking back at the Cold War. 

For several decades, successive U.S. administrations successfully convinced both the Soviet Union and its NATO allies that it would fight a nuclear war and accept massive Soviet nuclear attacks on the United States itself in order to defend Western Europe. That worked because friend and foe alike believed that Washington saw the security of Western Europe as literally vital to America’s own survival in the face of the Soviet Union’s seemingly formidable power. As Thomas Schelling memorably put it in his 1966 book Arms and Influence, extended deterrence was credible in that era because all parties believed that for America, defending its allies in Europe was “defending California.” Only that made it credible that America would accept a nuclear attack on its own cities in order to defend its allies.

This clarifies the question at the heart of U.S. extended deterrence towards South Korea today in light of Pyongyang’s ability to launch a nuclear strike on the United States. Is America’s stake in the security of South Korea today comparable to its stake in the security of Western European allies during the Cold War? In other words, is South Korea’s security from the North literally vital to America’s own security in the Western Hemisphere? Could a North Korean victory over South Korea credibly lead to a looming direct threat to the United States itself—the way a Soviet victory in Western Europe could well have done?

This is a significant and complex question. What made the Soviet threat to Western Europe a truly existential question for America was the very real prospect, especially in the Cold War’s early decades, that if the Soviets took over Western Europe, they could go on to dominate the whole of Eurasia, and thereby put itself in a position to overpower America itself and dominate the world. Clearly, North Korea simply could not pose that kind of threat, with or without South Korea’s resources. But that is not the end of the matter. Failing to fulfill its extended deterrence commitments to Seoul would arguably destroy U.S. leadership throughout East Asia and beyond and fatally undermine the post-Cold War international order that that leadership underpins.

Would this create a credible looming existential threat to America’s own security? That depends on what might take the old order’s place. The answer would be “yes” if there were a serious danger that, in the absence of U.S. leadership, a single authoritarian hegemonic power could come to dominate Eurasia the way the Soviet Union threatened to do in the late 1940s and 1950s. Though some see this outcome foreshadowed by today’s “no limits” partnership between Russia and China, the underlying realities of the distribution of wealth and power in the world today argue against it.

Much more likely is a multipolar global order in which a number of great powers—including China, India, Russia, Europe, and, of course, the United States—would balance and constrain one another. That would be much less congenial to Washington than the U.S.-led order of the post-Cold War era. Still, America would remain secure as the unchallengeable primary power in the Western Hemisphere. It is hard to see that it would make sense for America to fight a nuclear war to avoid this outcome—even assuming that such a war could be “won” and the old U.S.-led order preserved. To put it simply, but not inaccurately, America has a truly vital interest in maintaining its Monroe Doctrine primacy in the Western Hemisphere. In an era of strategic rivalry among multiple nuclear-armed great powers, it does not have a truly vital interest in perpetuating the U.S.-led global order of the post-Cold War era nor in sustaining the alliances that supported that order. 

These complex questions must trouble many U.S. allies as they consider how far they can rely on U.S. strategic commitments in the decades ahead. Still, they are especially urgent for policymakers in Seoul. Without a clear and compelling existential U.S. imperative to contain North Korea, there is arguably nothing Washington can do to assure South Koreans that they can depend on America to deter a nuclear attack from the north or neutralize North Korean nuclear blackmail. That would be so even if the very real prospect of a second Trump presidency did not raise questions about whether America will even try to provide that assurance or will instead abandon strategic commitments to allies like South Korea.

This brings us back to the question of what South Korea can do, given that there is no clear way to strengthen the credibility of U.S. extended deterrence. It faces a stark choice between developing a nuclear deterrent or living with the ever-increasing risk of North Korean nuclear blackmail—a risk made all the more salient by Pyongyang’s newly hostile rhetoric. This is why President Yoon spoke out about the nuclear option and why so many South Koreans support it. The seemingly inescapable conclusion is that it is possible—even probable—that Seoul will build its own nuclear weapons within the next few years. Of course, that would endanger its  U.S. alliance, but Seoul might well decide that a nuclear deterrent is more important to its security. Indeed, once South Korea develops a nuclear weapons program, the costs of the alliance might well outweigh the benefits.

This would, of course, have consequences beyond the Korean Peninsula. It would be a major blow to the non-proliferation efforts around the world, but the most significant effect would be just across the Straits of Tsushima. A decision by Seoul to go nuclear would amplify Japanese doubts about the credibility of U.S. extended nuclear deterrence and greatly increase pressure on Tokyo to go nuclear, too. That would then raise questions about the future of the U.S.-Japan alliance, and not just from the  U.S. side. Like Seoul, Tokyo would have to ask whether the benefits of the alliance still outweigh the costs when Japan no longer needs to depend on U.S. extended nuclear deterrence. It is far from clear that the answer would be “yes.”

And this, of course, would have immense implications for the future of America’s entire strategic posture in East Asia and the Western Pacific. Here is the key underlying significance of North Korea’s newly bellicose language towards the South. By deepening South Korea’s fear of North Korean nuclear blackmail, Pyongyang has sharpened Seoul’s doubts about  U.S. extended deterrence, pushed Seoul towards building its own nuclear weapons, and arguably nudged Japan in the same direction. All this exposes and increases the fragility of the two key alliances on which America’s entire strategic position in East Asia and the Western Pacific depends.

And that, perhaps, is exactly what Pyongyang intends. At first glance, it might seem that its interests would not be served by encouraging Seoul to go nuclear. But look closer. On the Peninsula itself, facing a choice between a nuclear-armed South Korea or a nuclear-armed United States across the DMZ, it makes sense for them to choose the former. Looking beyond the Peninsula, it surely serves North Korea’s interests to undermine America’s strategic position in the wider region. It certainly serves the interests of North Korea’s most important neighbors, partners, and supporters, China and Russia, whose principal ambition is to reduce and, if possible, eliminate America’s strategic weight and influence in regions close to their borders. And that may ultimately be what Pyongyang’s new brand of tough talk towards South Korea is really all about.

About the Author: Dr. Hugh White

Hugh White is an Emeritus Professor of Strategic Studies at the Australian National University in Canberra.

Main Image is from U.S. Air Force. All Other Images: KCNA/Screenshot.