The 38th parrallel

Answer 1

See "Korean War"

It is the parallel of latitude that in East Asia roughly demarcates North and South Korea . The line was chosen by the U.S. at the Potsdam Conference, in July 1945, as an army boundary, north of which the U.S.S.R. was to accept the surrender of the Japanese forces in Korea and south of which the Americans were to accept the Japanese surrender. The line was intended as a temporary division of the country, but the onset of the Cold War led to the establishment of a separate U.S.-oriented regime in South Korea under Syngman Rhee and a communist regime in North Korea under Kim Il-sung. After the onset of the Korean War between North and South Korea in June 1950, United Nations forces, which, under U.S. general Douglas MacArthur, had come to the aid of the south, moved north of the 38th parallel in an attempt to occupy North Korea. With the intervention of Chinese troops, the war came to a stalemate roughly along that parallel. The cease-fire line, fixed at the time of the armistice agreement, gave South Korea possession of an eastern mountainous area north of the parallel, which was the major battlefront when the demarcation line was fixed.