► The persistence of North Korea in enhancing its nuclear arsenal, coupled with its demonstrated ability to launch ballistic missiles underlines an imminent and formidable threat to the national security of South Korea.

► The prospect of achieving complete and verifiable denuclearization seems increasingly remote. Thus, South Korea needs to adapt its military and diplomatic strategies, acknowledging the growing possibility that North Korea's nuclear armament could become an irreversible reality at least for the near future.

► The objectives of South Korea's strategies are to minimize the chance of North Korea initiating a war, aim to decrease North Korea's expected payoff of war relative to that of the (peaceful) status quo, strengthen the U.S. extended deterrence to South Korea, and for the country to develop its own deterrence mechanism.

► South Korea's leaders should focus on actual defense and deterrence measures and refrain from unnecessarily escalating regional tensions by overly ideologizing and politicizing its security strategies.

Over recent decades, the Korean Peninsula has seen an escalation in tensions primarily driven by North Korea's aggressive development of nuclear weapons and missile technologies. These advancements not only defy numerous international sanctions but also stand as a direct challenge to regional stability, particularly for South Korea. The persistence of North Korea in enhancing its nuclear arsenal, coupled with its demonstrated ability to launch ballistic missiles underlines an imminent and formidable threat to the national security of South Korea. Additionally, in September 2022, the Supreme Peoples' Assembly of North Korea adopted a law that broadens the conditions under which it might use nuclear weapons, including a potential first strike in situations threatening the regime's survival.

Efforts to denuclearize North Korea through economic sanctions and diplomatic negotiations have largely been ineffective. While the goal of denuclearizing North Korea should not be abandoned, the prospect of achieving complete and verifiable denuclearization seems increasingly remote. South Korea, therefore, needs to adapt its military and diplomatic strategies, acknowledging the growing possibility that North Korea's nuclear armament could become an irreversible reality at least for the nearble future. This essay delves into South Korea's strategies and the critical considerations accompanying them.

The primary objective of South Korea's strategies is to minimize the chance of North Korea initiating a war. To comprehend what factors influence war probabilities, we must understand the plausible scenarios that might lead to clashes on the Korean Peninsula. The decision-makers for starting a war are primarily Kim Jong Un and other top leaders in North Korea. I posit that their motives align with typical political elites in most authoritarian states; their main aim is to preserve their political power.  Yet, given that North Korea's military power is significantly inferior to the combined strength of the South Korea-U.S. alliance, any war action is an extremely risky move for Pyongyang. Such a decision carries a high likelihood of leading to the regime's collapse, which would be the most unfavorable outcome for the North Korean leadership. One might hastily deduce that North Korea would never choose war, but that is a misguided conclusion since war is just one way for the regime to collapse. There might be circumstances, like intense domestic political upheaval, where the leadership feels the regime's continuity is untenable, making military aggression seem like a relatively viable option to retain power. In essence, conflict might arise when the North Korean leaders perceive peaceful regime sustenance as less beneficial compared to the potential gains from war.

South Korea then should aim to decrease North Korea's expected payoff of war relative to that of the (peaceful) status quo. Evidently, two approaches are possible: to lower the former and to raise the latter. A way to increase North Korea's expected payoff of peace is to enhance diplomatic and economic cooperation between the two Koreas. While this approach has its merits, I am skeptical that the conciliatory method alone can guarantee lasting peace and stability on the Korean peninsula. I contend that a distinct characteristic of the North Korean state is its heavy reliance on ideological rallying, which often involves adopting an antagonistic stance toward the U.S. and South Korea in order to cement its legitimacy among its own people. If the North Korean regime occasionally requires international disputes to meet domestic political ends, a solely diplomatic approach will have limited effectiveness.

Thus, my emphasis will be on diminishing North Korea's prospect of war, which leads to a focus on the strategy of deterrence. Historically, South Korea's nuclear deterrence has mostly relied on the U.S. nuclear umbrella. However, North Korea's recent advancements in nuclear weapons and delivery systems pose significant challenges to the U.S.'s extended deterrence commitments to South Korea. Essentially, North Korea's nuclear prowess questions the U.S.'s readiness to endanger its own cities in defense of Seoul. It seems that North Korea's pursuit of advanced ICBM technology aims to disrupt the close security relationship between South Korea and the U.S. By presenting a genuine threat to the U.S. homeland, North Korea might believe that the U.S. would hesitate before intervening in a regional conflict, thereby undermining the alliance's overall deterrence strength.

How would South Korea respond to such a challenge? There are two options that are complementary to each other. One is to strengthen the U.S. extended deterrence to South Korea, and the other is to develop its own deterrence mechanism.

The effectiveness of the extended deterrence is contingent upon the alliance's commitment to retaliate being credible. The credibility in turn hinges on whether it would be rational for the U.S. to retaliate should South Korea come under attack. It should be noted that credibility is not a dichotomous variable. War may occur in many different circumstances, and whether the U.S. leaders' decision to retaliate with full force is consistent with their own interests depends upon various factors including the state of South Korea-U.S. relation, public opinion in the U.S., military strengths of North Korea, the anticipated reactions of other states, and so on. Thus, we can say that a policy enhances credibility of the extended deterrence if the policy makes the U.S.'s retaliation an optimal response in some marginal circumstances where it would not be so without the policy.

In this sense, the Washington Declaration and subsequent creation of the Nuclear Consultative Group (NCG) strengthen the credibility of the U.S.'s extended deterrent promises. The declaration itself will raise the U.S.'s audience cost of reneging its commitment. Institutionalization of the NCG will mitigate the informational asymmetry between the patron and the client of the extended deterrence relationship. Generally, by increasing South Korea's decision-making influence in the alliance's response to potential aggression from North Korea, the credibility of the extended deterrence will be enhanced. This is because South Korea possesses a stronger resolve than the U.S.

However, while enhancing the U.S.'s extended deterrence towards South Korea is important, it might not be entirely sufficient to prevent North Korea's aggression. A few years back, South Koreans witnessed firsthand the unpredictability of the U.S.'s decisions concerning the Korean Peninsula. This was evident when the Trump administration unilaterally threatened to strike North Korea and attempted to reduce the U.S.'s military presence on the peninsula with exorbitant demands over cost-sharing. Given the polarized nature of the current U.S. domestic politics and its susceptibility to populist sentiments that prioritize narrow national interests, it is risky for South Korea to solely rely on the extended deterrence. Its credibility can fluctuate based on the election outcomes in the U.S., which North Korea is keenly aware of.

South Korea thus must cultivate its own deterrence capabilities. I do not argue for South Korea's nuclear armament. Such a move would not only be regarded as a formal abandonment of the denuclearization of the Korean Peninsula, but it would also undermine the South Korea-U.S. alliance that is currently central to South Korea's security and stability of East Asia. 

However, as part of its self-defense strategy, South Korea should focus on refining its independent counterforce and countervalue tactics using advanced conventional weaponry. While it's a challenge for a non-nuclear state to deter a nuclear-armed adversary using only conventional means, modern technological breakthroughs have made conventional counterforce and countervalue approaches notable threats to nuclear arsenals. South Korea has consistently bolstered its independent  deterrence measures. Its counterforce strategies, which include the Korean Air and Missile Defense system, the Kill Chain, and the Korean Massive Punishment and Retaliation strategy, have been continuously improving as the U.S. has relaxed restrictions on South Korea's missile capabilities a few times.

While the challenge of the U.S.'s extended deterrence is centered on resolve, the challenge for South Korea's own deterrence lies in its capabilities. Much of South Korea's military technology relies on the U.S., particularly evident in its dependence for intelligence, surveillance, and reconnaissance resources. Therefore, South Korea currently frames its independent strategy within the context of the alliance. Nonetheless, South Korea is steadily inching toward acquiring an independent counterforce capability.

Another key consideration is that South Korea's progress in conventional deterrence technology will enhance its nuclear potential. The skills and capabilities South Korea gains from developing its conventional deterrence can make it easy to obtain a nuclear deterrence if circumstances require the country to consider becoming a nuclear state. A strong nuclear latency not only positions South Korea to better respond to threats from North Korea but also motivates the United States to reinforce the reliability of its extended deterrence. There is a critical difference between lacking the ability to be a nuclear state and making a strategic decision not to be.

Thus far my discussion on deterrence strategies has focused primarily on their military aspects and immediate strategic impacts. Yet, strengthening the deterrence strategies may have long-term consequences for stability in East Asia. Specifically, there might be concerns that increasing military capabilities of the South Korea-U.S. alliance would provoke North Korea and other regional actors including China, potentially leading to a further escalation in tensions. 

On this topic, I would like to make two points. Firstly, we must admit that a degree of escalation is unavoidable given the current East Asian strategic dynamics. With North Korea's anticipated advancements in nuclear and missile capabilities and the increasing tension between the U.S. and China, risk of regional conflicts are likely to grow, independent of South Korea's decisions. The primary focus of South Korea should be to address threats directed towards it.

Secondly, while South Korea must take necessary measures for its protection, it is crucial to avoid unnecessary provocations. Actions should be aimed at genuinely bolstering its defense without the need to escalate tensions through heightened rhetoric. South Korea's leaders should refrain from unnecessary confrontations by not overly ideologizing and politicizing their security strategies.

In the face of North Korea's unyielding advancements in nuclear and missile technologies, South Korea is at a pivotal moment in shaping its defense strategies. In this essay, I have emphasized the need for South Korea to reinforce the U.S.'s extended deterrence and to enhance its indigenous defense capabilities without completely abandoning the core principles of denuclearization. Hopefully, striking this delicate balance reinforces South Korea's immediate security against the threats from the North and helps in maintaining stability in the broader East Asian region. Also, while enhancing deterrence is imperative, South Korea must act prudently to prevent its initiatives and rhetoric from inadvertently escalating regional tensions.