Korea had gotten roped into the Russo-Japanese War. Korea was then annexed by Japan in 1910 and were ruled over for decades.
They were the ones who made the decision that Korea would be divided into North and South Korea while trying to help stabalize Korea and get rid of the Japanese forces staying there.
Korea was divided in half.
It was the conference where the decision of where the line would be was made.
It started when in 1950 North Korea invaded the South after tensions had been growing on both sides.
It ended in 1953 when a truce was made but they were techically still at war since there was no formal declaration of peace.
It is the dividing line between North and South Korea and runs from the Han River on the Western side to the North Korean town of Kosong on the East. It was created when the U.S. and the USSR found a middle point where Korea would be divided in 1945.