NORTHERN LIMIT LINE IN THE YELLOW SEA: FROM AN INTER-KOREAN DISPUTE TO A POTENTIAL INTERNATIONAL CONFLICT 

Anastasia O.Barannikova

Admiral Nevelskoy Maritime State University, Vladivostok 

Abstract: The Northern Limit Line (NLL), established in 1953 in the Yellow (West) Sea, has for decades remained one of the most conflict-prone elements of security on the Korean Peninsula. Being a de facto maritime border established unilaterally after the Korean War, the NLL has never been recognized by the Democratic People’s Republic of Korea (DPRK) and has repeatedly been the cause of armed incidents between the DPRK and the Republic of Korea (ROK). In the context of Pyongyang’s official abandonment of the policy of unification on the Korean Peninsula and the consolidation of the concept of “two Korean states,” the dispute surrounding the NLL is increasingly transforming from an inter-Korean issue into an international maritime territorial dispute with a high risk of escalation and internationalization. Given the allied treaties between the ROK and the United States, and between the DPRK and China and Russia, armed incident in the area of the NLL carries the risk of rapid horizontal and vertical escalation of the conflict. This article examines a brief history of the dispute, the current situation, potential escalation scenarios and explores possible pathways for de-escalation. It uses the terms “Yellow Sea” and “West Sea” as functionally equivalent. In international practice and English-language sources, the term Yellow Sea predominates, while official rhetoric in the DPRK and the Republic of Korea widely uses the term West Sea (서해, 조선서해).

Keywords: Northern Limit Line, Yellow Sea, DPRK, ROK, maritime boundaries, regional security

History of the problem

          The Northern Limit Line was established on August 30, 1953, by the United States-led UN Command shortly after the signing of the Korean Armistice Agreement. The armistice document defined a land demarcation line (the Military Demarcation Line), but did not clearly define the maritime boundary in the Yellow/West Sea. In the absence of an agreed-upon mechanism, the UN command unilaterally, without consulting Pyongyang, drew a Northern Limit Line (NLL) that was extremely disadvantageous to North Korea, denoting it within three nautical miles (5,556 m) of the North Korean coast. As a result, five islands (Baengnyeongdo, Taechongdo, Socheongdo, Yeonpyeongdo, and Udo) south of the NLL came under ROK control—at that time, under UN control. The line was not included in the 1953 armistice and has no international legal basis, yet the ROK and the US still rely on the 1953 demarcation. 

The DPRK has never recognized this line, which seriously limited its activities in the waters of Ganghwa (Gyeonggi) Bay and blocked free access to areas rich in marine bioresources. In the late 1950s, the North Korean leadership proposed establishing a 12-nautical-mile (18,584 m) military demarcation line extending from the southwestern coast of the DPRK and running strictly diagonally between Hwanghae Province (North Korea) and Gyeonggi (South Korea) in the Yellow Sea. However, Seoul refused to change the 1953 demarcation for security reasons. In December 1973, the DPRK drew up new maritime border that included five islands, which were under South Korea’s control at that time, including Yeonpyeong and Baekryeong islands, in the DPRK’s territorial waters. Both the ROK and DPRK, based on international maritime law, adopted unilateral legislations establishing 12-mile territorial waters and exclusive economic zones in the Yellow Sea, including Ganghwa (Gyeonggi) Bay [3]. These steps resulted in a maritime territorial dispute. The disputed area is of great economic and military significance: the waters of the Yellow Sea are rich in fish resources, and control over the water area is important for the safety of navigation and military communications. The NLL passes through an active fishing zone which is of vital importance to the DPRK and is located near Incheon, one of ROK’s largest ports.

Table 1. Officially adopted names of the demarcation line in the Yellow/West Sea

Country	Original language	English translation
DPRK	조선 서해 해상  군사분계선	Korea West Sea Maritime Military  Demarcation line, KWSMMD
China	北方界线	Northern Boundary
ROK	북방한계선	Northern Limit Line, NLL
International		Northern Limit Line, NLL

  Source: compiled by author

In October 1999 the DPRK finally declared its own “Inter-Korean MDL in the Yellow Sea,” running south of the NLL and including the five islands in DPRK’s territory. North Korean leadership also defined a military protection area coinciding with the boundary of its exclusive economic zone (EEZ) in the Yellow Sea. Since then, the area has become the scene of regular clashes, including armed incidents [6].

Table 2. Significant incidents in the disputed area

Date	Incident	Description	Losses on both sides
June 15, 1999	First Battle of Yeonpyeongdo	Confrontation at sea between N. Korean and S. Korean patrol boats along a disputed maritime boundary near Yeonpyeong Isl.	1 torpedo boat sunk 6 patrol boats damaged 1 corvette damaged 17–30 killed ~79 wounded
June 29, 2002	Second Battle of Yeonpyeongdo	Confrontation at sea between N. Korean and S. Korean patrol boats along a disputed maritime boundary near Yeonpyeong Isl.	1 patrol boat sunk 1 patrol boat damaged 19 men killed 43 wounded
November 10, 2009	Battle of Daecheong	Clash between the S.Korean and N.Korean navies near the disputed line off  Daecheong Isl.	1 gunboat damaged 1 patrol boat damaged 8 wounded
March 26, 2010	ROKS Cheonan sinking	Sinking of ROK’S Cheonan during the ROK-US joint anti-submarine warfare exercises (part of the Key Resolve/Foal Eagle war exercise). The DPRK was blamed but denied involvement.	46 killed 58 wounded ROK’S Cheonan sunk
November 23, 2010	The Bombardment of Yeonpyeongdo	An artillery engagement between the N. Korean military and S. Korean forces stationed on the island	4-20 people (military personnel and civilians) were killed on both sides ~ 40–55 wounded

Source: compiled by author

Current situation and dynamics of tensions

         By now, the border dispute between North Korea and South Korea in the Yellow or West Sea remains unresolved, creating conditions for periodic provocations on both sides. In addition to the continuing economic and military importance of the water area, the situation is aggravated by domestic and foreign policy factors. It can be argued that the potential for conflict has only increased in recent years. This was largely due to changes in both Korean states and the dynamics of inter-Korean relations. 

In 2022, a conservative government came to power in the Republic of Korea, which took a course of exacerbating relations with the DPRK. The DPRK, in its turn, reviewed its policy on the Korean Peninsula. At the end of 2023, Kim Jong-un declared that he no longer considered unification with the Republic of Korea possible. The 10th session of the 14th Supreme People’s Assembly of the DPRK in January 2024 legalized the new policy «on the basis of putting an end to the nearly 80 year-long history of inter-Korean relations and recognizing the two states both existing in the Korean Peninsula».  As for the NLL, it was stated that «as the southern border of our country has been clearly drawn, the illegal “northern limit line” and any other boundary can never be tolerated, and if the ROK violates even 0.001 mm of our territorial land, air and waters, it will be considered a war provocation» [5]. 

As a result, if previously the unsettled border disputes in the NLL area, like any other unsettled border issue between the two Korean states, was considered an intra-peninsular conflict that could be resolved politically in the context of future unification, now it is taking on the features of a classic international maritime territorial dispute between the two independent states in hostile relations. The overthrow of conservative president in the ROK did not improve the situation; the DPRK perceives the Republic of Korea as a state deprived of sovereignty, regardless of the government. Moreover, recent years have seen a degradation of inter-Korean military communication channels, the virtual collapse of tension reduction agreements reached in 2018–2019, and the absence of any bilateral fisheries agreements, as seen in other countries in the region.

Additional factors of instability include geopolitical rivalry between the US and China. Yellow Sea is not only the arena of clashes between Korean states. It is also a place where interests of China and US collide, with the presence of the latter provided via ROK. In response to the US presence around the Korean Peninsula China has intensified its activity here including military one. Suffice is to recall so-called «wars of the buoys» with South Korea in the Korea-China Provisional Measures Zone (PMZ) [4], Chinese warplanes flying near its airspace, drills with the Fujian aircraft carrier and other actions raising concerns in ROK [1]. Moreover, each activity of China is perceived as mirroring that in the South China Sea and thus aimed at deterring US and allies. 

The Cold War-style blocs that have formed in the region as a result of the rivalry between the US and China and the collective West and Russia (both China and Russia are allies of the DPRK) also do not contribute to the easing of tensions. China is not formally a party to the dispute in question, but it also does not recognize the NLL as an international legal boundary and rightly perceives US steps to allegedly deter the DPRK as steps to contain China itself. While the United States has a significant influence on the ROK’s position on the NLL, China can be considered to have a similar influence on the DPRK’s position.

Potential escalation scenarios

Disputed maritime boundaries can be considered an ideal pretext for escalation. While crossing a land border is clearly viewed as act of aggression, unilateral delimitation of waters, non-military occupation of disputed islands, or making some installations is not  always perceived as a direct threat. At the same time unsettled maritime dispute provides conflicting parties with a number of escalatory maneuvers and has a relatively low threshold for conflict initiation. Acts of underwater sabotage, limited military operations aimed at seizing strategically significant islands, provocations, false-flag operations, or secret operations like SEAL Team 6 mission of 2019 [2] are all possible future scenarios. As the conflict potential of the NLL rises, it makes sense to consider possible scenarios of escalation. 

At present, the scenario of a conflict due to the notorious “human factor” seems most likely. This may be facilitated by the psychological breakdown in the military of both conflicting sides due to constant stress, prolonged effects of propaganda, multiplied by the fog of war and absence of communication lines. The conflict may start with “misinterpreted signal” when, due to a combination of circumstances, one side’s actions are perceived by the other as an attack. A short-term violation of a maritime border (which, as is known, each side interprets in its own way) or the airspace of another country, a collision between patrol boats or fishing vessels, accompanied by limited use of force, are also possible. Similar incidents have occurred repeatedly in the past and can quickly spiral out of control in the absence of communication. Since such a scenario would most likely arise against the will of the countries’ leaders, it should be expected that these leaders will take all measures to prevent the escalation of the conflict.

Deliberate provocations by one side or another are much less likely, although they should not be ruled out. For example, the DPRK or ROK may stage some action at the request of China or the US, respectively, to distract the opponent’s attention from another region. In the case of South Korea, provocation by some political forces is possible, who are in opposition to the current administration, primarily far-right South Korean «activists».  The current government of the ROK could only resort to deliberate provocation in the Yellow Sea if it would benefit the US, and the latter is currently focused on other regions of the world.  At the same time no government of the ROK would be interested in a full-fledged conflict with the DPRK, if only because it is within the effective range of most North Korean weapons systems, including tactical nuclear weapons. A provocation/conflict initiated by the DPRK, or even an excessive response to a provocation by the ROK, is also unlikely, if only because the DPRK must now take into account the interests of not only China, but also Russia, which, although not a direct participant in the NLL affairs, will be involved in potential conflict as an ally of the DPRK. This is evidenced, for example, by North Korea’s reaction, or rather lack thereof, to the provocations of the former Yoon government. 

Overall, none of the countries of the region is currently interested in a full-scale military conflict. Therefore, if an armed incident, say, due to human factor, occurs, all major powers in the region will be interested in preventing its horizontal and vertical escalation. The conflict between the Korean states is dangerous because it could quickly be internationalized. Republic of Korea and the DPRK have allied treaties with the United States and China and Russia, respectively. US-China and US-Russia relations are tense and most of the parties of the conflict are nuclear-armed, so a serious conflict between the Korean states, could easily escalate into a third world war, even with the participation of nuclear weapons – the worst-case and unacceptable for all countries scenario.

Ways to resolve a dispute

Given the high conflict potential of the disputed NLL, it requires careful and continuous crisis management. A full legal settlement of the dispute is unlikely in the short term given the tense relations between two Korean states and conflicting interests of external actors. The so-called great powers are interested in resolving the dispute between Korean states no more than in escalating it to a full-fledged conflict. However, there are some prospects for a long-term resolution. One option involves a bilateral settlement between the DPRK and ROK and could include:

– Restoring military communication channels between the DPRK and ROK to prevent unintended escalation.

– Creating temporary joint fishing zones, which were previously discussed during the inter-Korean dialogues in the past.

– Transparency measures and notification of military exercises and live fire near the disputed zone.

One of the key barriers to a peaceful settlement along the Northern Limit Line is competition for marine resources, particularly the valuable commercial species of the West Sea. This competition exacerbates confrontation and contributes to frequent crossings of the disputed line by both military and civilian vessels, increasing the risk of incidents. 

Establishing even temporary fishery cooperation or joint management zones would reduce tensions along disputed maritime boundary by ensuring:

– joint regulation of fishing and quota allocation;

– mechanisms for data exchange and notification of civilian vessel movements;

– joint or multilateral maritime patrols within a demilitarized framework;

– channels for preventing and de-escalating conflicts at sea.

Such mechanism could be a practical step toward building trust between the DPRK and ROK, reducing the likelihood of an accidental escalation to an international military conflict.

Provided there is a positive dynamic in relations between the Korean states further steps could include border settlement between two Korean states with taking into account changes in both countries’ policies regarding unification and concluding fisheries agreement on the regular basis by example of existing agreements between other countries of the region.

The second option involves a multilateral consultation format involving the US and China on maritime security in the Yellow Sea and could include:

– Revising the maritime boundary between the DPRK and ROK to reflect the new normal— the existence of two independent states on the Korean Peninsula

– Working out crisis management measures and possibly, creating some kind of international security mechanism.

It should be understood that any real mechanism between the two Korean states will hardly be bilateral, given the strong influence of big powers and their interests in the region. Just as a conflict between the Korean states would inevitably become internationalized, their rapprochement would also trigger interference by countries having interests in the region. As has already been said, China is also a Yellow Sea country and its opinion must be taken into account. US is not but it has strong influence on the ROK, the participant of the NLL maritime dispute. Both the US and China have far-reaching geopolitical and military-strategic plans for the Yellow Sea, benefit from maintaining tensions between the DPRK and the ROK for as long as possible viewing Korean Peninsula as a buffer and a lightning rod in their own geopolitical rivalry. So, it is difficult to imagine that big powers would facilitate the dialogue between two Korean states for resolving military, political and border issues in the near future. They will rather prevent this dialogue. The US will exert every possible pressure on Seoul to avoid making any concessions to Pyongyang. Pyongyang, in its turn, will be supported and influenced by Beijing.

As a result, countries that could contribute to stabilizing situation in the West/Yellow Sea will in fact cause additional obstacles with their conflicting interests, tense relations and their strong influence on regional countries. From this point the most effective way to resolve NLL issue would be negotiations between the DPRK and ROK based on bilateral relations without the interference of third parties. But it would require strong political will and sovereignty (especially true for the ROK).

To conclude, the Northern Limit Line in the Yellow Sea remains one of the potential flashpoints in East Asia. The transformation of inter-Korean relations and the retreat from the concept of reunification are giving this maritime dispute a new, international dimension. Given the fierce confrontation between blocs in NEA and the weakening of dialogue mechanisms, even a limited incident could have disproportionately serious consequences. At the same time, the likelihood of a serious military conflict currently remains low, since all involved countries are interested in preserving status-quo. Therefore, what is needed is not so much an immediate resolution of the territorial issue, but rather the development of sustainable mechanisms for crisis prevention and joint resource management that would facilitate a peaceful resolution of the dispute on the basis of international maritime law.

REFERENCES:

1.China’s West Sea gambit, “The Korea Times”. June 9, 2025, URL: https://www.koreatimes.co.kr/opinion/editorial/20250609/china-slammed-for-infringing-on-koreas-sovereignty-in-west-sea

2.Dave Philipps and Matthew Cole. How a Top Secret SEAL Team 6 Mission Into North Korea Fell Apart, “The New York Times”, September 5, 2025, URL: https://www.nytimes.com/2025/09/05/us/navy-seal-north-korea-trump-2019.html

3.Ivanov Alexander Yuryevich The demarcation line between the DPRK and the Republic of Korea in the Yellow Sea as a factor of tension on the Korean Peninsula // Russia and Asia Pacific, 2017, №2 (96), URL: https://cyberleninka.ru/article/n/razgranichitelnaya-liniya-mezhdu-kndr-i-respublikoy-koreya-v-zhyoltom-more-kak-faktor-napryazhyonnosti-na-koreyskom-poluostrove 

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5.Respected Comrade Kim Jong Un Makes Policy Speech at 10th Session of 14th SPA,  KCNA. January 16, 2024, URL:  http://kcna.kp/en/article/q/f4bf631617198851f067bd66d7f48d18.kcmsf

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