The Korean War began on June 25, 1950, when Communist-backed North Korea attacked South Korea. Led by the United States, the United Nations demanded that North Korea withdraw across the 38th parallel and authorized member nations to send troops to assist South Korea. The United States immediately sent inexperienced, unprepared Army troops from Japan. Early in the fighting, U.S. and South Korean forces made a courageous stand at the Pusan Perimeter before U.S. Gen. Douglas MacArthur launched a surprise attack behind enemy lines at Inchon, causing the North Koreans to split their forces and allowing U.S. and South Korean armies to push inland, recapture Seoul, and drive North Korean forces back across the 38th Parallel. When United Nations forces pushed farther into North Korea, Communist China entered the war, catching American troops by surprise and leading to a desperate campaign at the Chosin Reservoir and a heroic withdrawal to Hungnam, events cited as among the most significant battles in United States Marine Corps history. The war then entered a phase of numerous smaller but brutal battles for strategic positions while truce talks continued at Panmunjom for more than a year even as fighting went on. In the summer of 1953, a truce agreement was signed, and on July 27, 1953, it reset the boundary between North and South Korea at the 38th parallel, provided for the exchange of POWs, and called for elections to reunite the two Koreas, which as of 2017 had not occurred. The war was significant as the first time a world organization united to fight back an aggressive nation; twenty-one United Nations countries participated, including sixteen that sent military personnel. It also marked the first use of helicopters to evacuate wounded to M.A.S.H. hospitals and for low-level ground support, and the first all-jet aerial combat. Historians have also cited the war and the friction it caused between the Soviet Union and Communist China as a factor in the later downfall of Communism. The war was brutal for all countries involved: nearly 37,000 U.S. personnel were killed in Korea, more than 8,000 servicemen remained missing in action, and almost 200,000 U.S. servicemen were sent to Korea. South Korea suffered enormous devastation, but its recovery has continued to be miraculous, and what was once called the forgotten war is now remembered as a great victory for democracy.