The 38th parallel was first suggested as a dividing line for Korea in 1902. Russia and Japan were both attempting In an attempt to prevent any conflict, Japan proposed to Russia that the two sides split Korea into separate spheres of influence along the 38th parallel. However, no formal agreement was ever reached, and Japan later took full control of Korea.
After the surrender of Japan in 1945, the parallel was established as the boundary by the US State-War Navy Coordinating Committee in Washington, days before the complete liberation of Korea. The parallel divided the peninsula roughly in the middle. In 1948, the dividing line became the boundary between the newly independent countries of North and South Korea. After the ceasefire that effectively ended the Korean War (1950-1953), a new border was established through the middle of the Demilitarized Zone, which cuts across the 38th parallel at an acute angle, from southwest to northeast.
The 38th Parallel was also the place where the cease-fire was called to end the fighting. To this day, North and South Korea have never signed a formal peace treaty and thus are still officially at war; only a ceasefire was declared.