South Korea shares its only land border, separated by the Demilitarized Zone (DMZ), with which country?

The correct answer is North Korea. South Korea's only land border runs along the Korean Demilitarized Zone (DMZ), a roughly 250-kilometre-long, heavily fortified buffer strip that has separated the two Koreas since the armistice that ended active fighting in the Korean War in 1953. Despite its name, the DMZ is one of the most militarised borders on earth, lined with troops, fencing and landmines on both sides, and it runs close to the 38th parallel north, the original line along which the peninsula was divided after the Second World War. China, while a major neighbour of the broader East Asian region and North Korea's key ally, does not share a border with South Korea; it borders North Korea instead, and South Korea is separated from mainland China entirely by the Yellow Sea. Japan lies across the sea to the east of the Korean Peninsula, connected to South Korea only by maritime boundaries such as the Korea Strait, with no land border whatsoever. Mongolia, included as a distractor for its landlocked Inner Asian profile, lies far to the northwest and has no geographic proximity to the Korean Peninsula at all. A common exam confusion arises because South Korea is frequently discussed alongside China and Japan in East Asian regional blocs and trade groupings, tempting students to assume shared land borders that do not exist; in reality, South Korea's only land frontier is with North Korea, and all its other neighbours are separated by sea. Revision takeaway: remember that South Korea is a peninsular nation with exactly one land neighbour, North Korea, divided by the DMZ near the 38th parallel, while China and Japan are reached only by sea.