The North Korean invasion of the Republic of South Korea on 25 June 1950 advanced against an uncoordinated and ill equipped defence. The United Nations condemned the attack and the United States despatched air and ground forces in support of the retreating southern forces. Within two months the combined UN force was on the brink of defeat, holding a small enclave of territory that became know as the Pusan Perimeter. It was from this precarious position that a possible UN counter offensive would be launched. To relieve the Pusan Perimeter, General MacArthur, now UN commander, recommended an amphibious landing at Inchon, near Seoul and well over 100 miles (160 km) behind the KPA lines. The 250 ships of Task Force 7 transported X Corps, made up of 1st Marine Division, 7th Infantry Division and supporting units, a total of 40,000 troops. The landings began on 15 September; the subsequent advance through Inchon led to the recapture of Seoul, effectively cutting off the major lines of supply to the North Korean forces further south. Meanwhile, the now reinforced UN forces in the Pusan Perimeter began their breakout on 16 September, while UN air attacks on North Korean forces destroyed most of their tanks and artillery, forcing the survivors to flee northward. By 1 October UN troops passed the 38th parallel. On 7 October the United Nations authorized its forces to continue the advance into North Korea.
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