Complex sentence: It was 2,400 meters south of the Military Demarcation Line, which forms the border between South Korea (the Republic of Korea) and North Korea (the Democratic People's Republic of Korea).
Split into simpler sentences: It was 2,400 meters south of the Military Demarcation Line. The Military Demarcation Line forms the border between South Korea (the Republic of Korea) and North Korea (the Democratic People's Republic of Korea).