A supposedly 4-kilometer-wide strip of land cutting across the Korean Peninsula to separate the two Koreas, the Demilitarized Zone is a land of paradoxes. Despite its name, the DMZ is among the world’s most heavily fortified frontiers, with massive troop deployments and countless land mines on either side.

More than seven decades after its creation under the armistice that halted the three-year Korean War, the DMZ remains one of the Cold War’s most enduring flashpoints. Yet another paradox is that this volatile buffer zone lacks a clearly identifiable boundary on the ground. Instead, differing interpretations of an invisible line by three parties have created dangerous uncertainties.

Strictly speaking, the DMZ does have a legally defined boundary. The final battlefront of the war became the roughly 250-kilometer Military Demarcation Line, from which opposing forces were required to withdraw 2 kilometers on either side. The problem lies in translating that line, drawn by hand on maps attached to the armistice agreement, into precise coordinates on the ground. At a scale of 1:50,000, even a pencil stroke could represent a band several dozen meters wide.

The parties to the armistice — the US-led United Nations Command, North Korea and China — agreed to establish 1,292 numbered markers along the MDL. Installed under the supervision of the Military Armistice Commission, the yellow markers were maintained until 1973, when a South Korean soldier was killed by North Korean gunfire during maintenance work.

Scattered across mountains, valleys and marshes, the markers were never intended to define a permanent international border. Over the decades, many have disappeared or deteriorated amid shifting terrain and harsh weather. Meanwhile, the armistice supervisory mechanisms were weakened by institutional changes in the early 1990s.

Today, only about 200 markers are believed to remain identifiable, making much of the MDL difficult to locate precisely. South Korea and the UNC have developed operational reference lines using different combinations of armistice maps, surviving markers and modern geospatial data. North Korea, too, has established its own interpretation of the line.

These discrepancies have fueled recurring accusations of border incursions, raising the risk of accidental clashes. The stakes have risen further since North Korean leader Kim Jong-un abandoned his country’s long-standing pursuit of reunification and redefined inter-Korean relations as those between two hostile states in late 2023. The following year, he ordered extensive fortification of the southern border.

The campaign has brought North Korean troops increasingly close to the MDL. Barbed-wire fencing, construction of tactical roads and guard posts, vegetation clearing and mine laying do not necessarily violate the armistice as long as they remain on the permitted side of the line. Some of these measures may be intended as much to prevent defections and block South Korean influence as to strengthen military defenses.

Nevertheless, the Sept. 21 mine explosions that injured three South Korean soldiers near the western section of the MDL underscored the urgency of cross-border coordination. Sharing and verifying operational references — and ultimately reconciling their differences — could help prevent a cartographic dispute from escalating into an armed confrontation. Construction near an uncertain boundary, followed by warning shots over suspected crossings, presents a particularly dangerous combination.

Following a joint investigation with the UNC, South Korea’s military concluded that North Korean antipersonnel mines had been deliberately planted south of the MDL. Pyongyang vehemently denied responsibility, dismissing Seoul’s accusation as a fabricated incident. It also threatened to resume psychological warfare through loudspeaker broadcasts. North Korean artillery pieces subsequently appeared near the western border, their barrels pointed southward in an apparent show of force.

North Korea has ignored Seoul’s proposals for military talks to clarify the MDL, while pledging to press ahead with its border fortification campaign. Kim Yo-jong, the North Korean leader’s influential sister, has continued her verbal attacks, denouncing South Korea as a bitter enemy and hurling insults at the presidential staff.

Meanwhile, Seoul has begun addressing the MDL quandary. Amid repeated crossings by North Korean troops engaged in fortification work, the Defense Ministry proposed military talks in November 2025 and renewed its call following the September mine explosions. South Korea’s Joint Chiefs of Staff and the UNC have also undertaken efforts to compare and reconcile their operational references.

Establishing a common reference line between South Korea and the UNC would be an important first step. It would reduce confusion among forces operating south of the MDL and provide a more consistent basis for responding to suspected incursions.

More importantly, such coordination could lay the groundwork for eventual consultations with North Korea. Whether through three-way discussions or talks between the UNC and North Korea under existing armistice mechanisms, South Korea’s participation must be assured.

The MDL’s ambiguity is not merely a cartographic problem. It is a structural vulnerability in an already fragile security environment. At a time when dialogue is stalled and military tensions are mounting, even a modest effort to establish a shared understanding of the boundary could help avert an unintended confrontation. Clarifying the line that separates the two Koreas should not have to await a crisis.

Lee Kyong-hee

Lee Kyong-hee is a former editor-in-chief of The Korea Herald. The views expressed here are the writer's own. — Ed.


khnews@heraldcorp.com