What was used as the border between North Korea and South Korea?
INCORRECT
Imjin River
The Imjin River or Rimjin River is the 7th largest river in Korea.
It flows from north to south, crossing the Demilitarized Zone and joining the Han River downstream of Seoul, near the Yellow Sea. The river is not the namesake of the Imjin War (Japanese invasions in the late 16th century).
Image in the public domain.
38th Parallel
Gloster Hill