9. South Korea and North Korea

Border: Korean Demilitarized Zone (DMZ)
Area: 250 km* long, 4 km* wide
Est. Gross Domestic Product: $48.3 billion (North Korea) / $1.7 trillion (South Korea)*
The Korean Demilitarised Zone (DMZ), which stretches 250 km across the Korean Peninsula, is rife with watchtowers, landmines, and military personnel on both sides. It is far from being demilitarised. The DMZ, which was created in 1953 as a component of the Korean Armistice Agreement, represents the tension and unresolved situation between the two countries and acts as both a physical and metaphorical border.

Koreas, North, and South ©Michael Day using Wikipedia
The DMZ has ironically turned into an area of ecological value, with its undisturbed soil supporting a distinctive biodiversity despite the obvious threat of conflict. The DMZ is one of the most fascinating and complicated boundaries in the world because of the contrast between natural tranquilly and danger.