<human>:  When was the DMZ in North Korea built?
<bot>: The DMZ was built in the early 1950s, after the Korean War. It was intended to be a buffer zone between North Korea and South Korea. It is a strip of land along the 38th parallel, which separates the two countries. The DMZ is a 4.5 km wide strip of land, with a width of 1.5 km on either side. It is approximately 30 km long.