The world's most heavily guarded border is officially only an armistice line

A strip about 250 kilometres long and some four kilometres wide runs across the Korean peninsula. It is called the demilitarised zone. It is secured by fences, watchtowers and minefields. The name is the most precise understatement in world politics.

One legal point is the key to understanding it: the line is not a state border. It is the demarcation line of an armistice that officers from both sides signed at Panmunjom in 1953. No peace treaty followed. In terms of international law this war has been paused for more than seventy years. It was never ended.

How it came about

In 1945 the victorious powers divided the peninsula, until then occupied by Japan, along the 38th parallel, a line with no historical or geographical basis. The Soviet Union took over the administration in the north, the United States in the south. The administrative split became two states, and the people living there were not asked.

In 1950 the war began, and both sides pushed far beyond that line. In 1953 it ended without a victor and without peace, with an armistice and a demarcation line that runs roughly where the front last stood. That is why it no longer follows the 38th parallel but cuts across it at an angle. People living in the borderland found themselves on one side or the other depending on where the fighting had stopped.

The line does not mark where two states end. It marks where a front came to a halt.

— TerraTally · Borders desk

What became of the two halves cannot be described with equal confidence. South Korea grew into an industrial nation with an open society. Its border region is heavily secured and still economically part of the country, and the Seoul metropolitan area with its millions of inhabitants begins a few dozen kilometres south of the zone. Reliable data on North Korea are hard to come by. Much of what is reported rests on satellite images, accounts by people who fled, and estimates by international organisations. What is certain is that freedom of movement in the country is severely restricted and independent information is barely accessible.

The legal situation is unusual too. Most closely guarded borders separate states that recognise each other as states. Not here. South Korea's constitution describes the national territory as the whole Korean peninsula and its adjacent islands. The line therefore does not separate two territories but two claims to the same one.

Because the zone has barely been entered for more than seventy years, a strip of largely undisturbed nature has grown up there. Biologists document, from a distance and along the edges, species that have become rare or disappeared on the rest of the peninsula. The strip is not a nature reserve. It became one because nobody can get in.

That is the bitterest point of this border. It preserved a habitat by shutting out people who wanted to visit each other. Families were separated when the line was fixed, and many of them never met again. At the few reunions the two governments later allowed, siblings saw each other as old people for the first time since childhood. In law this line is a pause. The people have lived it as something final.