Eighth United States Army The Eighth United States Army ( EUSA ) , is a field army , the commanding formation of all United States Army forces in South Korea . A task force of troops which are composed of personnel from the Republic of Korea - United States alliance , it is based in Yongsan Garrison , in the Yongsan District of Seoul , South Korea . History . World War II . The unit first activated on 10 June 1944 in the United States , being commanded by Lieutenant General Robert Eichelberger . The Eighth Army took part in many of the amphibious landing s in the Southwest Pacific Theater of World War II , eventually participating in no less than sixty of them . The first mission of the Eighth Army , in September 1944 , was to take over from the U . S . Sixth Army in New Guinea , New Britain , the Admiralty Islands and on Morotai , in order to free up the Sixth Army to engage in the Philippines Campaign ( 1944 – 45 ) . The Eighth Army again followed in the wake of the Sixth Army in December , when it took over control of operations on Leyte Island on 26 December . In January , the Eighth Army entered combat on Luzon , landing the XI Corps on 29 January near San Antonio and the 11th Airborne Division on the other side of Manila Bay two days later . Combining with I Corps and XIV Corps of Sixth Army , the forces of Eighth Army next enveloped Manila in a great double - pincer movement . Eighth Army ' s final operation of the Pacific War was that of clearing out the southern Philippines of the Japanese Army , including on the major island of Mindanao , an effort that occupied the soldiers of the Eighth Army for the rest of the war . Occupation of Japan . Eighth Army was to have participated in Operation Downfall , the invasion of Japan . It would have taken part in Operation Coronet , the second phase of the invasion , which would have seen the invasion of the Kanto Plain on eastern Honshū . However , instead of invading Japan , Eighth Army found itself in charge of occupying it peacefully . Occupation forces landed on 30 August 1945 , with its headquarters in Yokohama , then the HQ moved to the Dai - Ichi building in Tokyo . At the beginning of 1946 , Eighth Army assumed responsibility for occupying all of Japan . Four quiet years then followed , during which the Eighth Army gradually deteriorated from a combat - ready fighting force into a somewhat soft , minimally - trained constabulary . Lieutenant General Walton H . Walker took command in 1948 , and he tried to re - invigorate the Army ' s training , but he was largely unsuccessful . This situation was to have serious consequences in South Korea . Korean War . The peace of occupied Japan was shattered in June 1950 when North Korea invaded South Korea , igniting the Korean War . American naval and air forces quickly became involved in combat operations , and it was soon clear that American ground forces would have to be committed . To stem the North Korean advance , the occupation forces in Japan were thus shipped off to South Korea as quickly as possible , but their lack of training and equipment was telling , as some of the initial American units were destroyed by the North Koreans . However , the stage was eventually reached as enough units of Eighth Army arrived in Korea to make a firm front . The North Koreans threw themselves against that front , the Pusan Perimeter , and failed to break it . In the meantime , Eighth Army had reorganized , since it had too many divisions under its command for it to exercise effective control directly . The I Corps and the IX Corps were reactivated in the United States and then shipped to Korea to assume command of Eighth Army ' s subordinate divisions . The stalemate was broken by the Inchon landings of the X Corps ( tenth corps , consisting of soldiers and Marines ) . The North Korean forces , when confronted with this threat to their rear areas , combined with a breakout operation at Pusan , broke away and hastily retired . Both South and North Korea were almost entirely occupied by United Nations forces . However , once American units neared the Yalu River and the frontier between North Korea and China , the Chinese intervened and drastically changed the character of the war . Eighth Army was decisively defeated at the Battle of the Chongchon River and forced to retreat all the way back to South Korea . The defeat of the U . S . Eighth Army resulted in the longest retreat of any American military unit in history . General Walker was killed in a jeep accident and replaced by Lieutenant General Matthew Ridgway . The overstretched Eighth Army suffered heavily with the Chinese offensive , who were able to benefit from shorter lines of communication and with rather casually deployed enemy forces . The Chinese broke through the American defenses despite American air supremacy and the Eighth Army and U . N . forces retreated hastily to avoid encirclement . The Chinese offensive continued pressing American forces , which lost Seoul , the South Korean capital . Eighth Army ' s morale and " esprit de corps " hit rock bottom , to where it was widely regarded as a broken , defeated rabble . General Ridgway forcefully restored Eighth Army to combat effectiveness over several months . Under his leadership , it slowed and finally halted the Chinese advance at the battles of Chipyong - ni and Wonju . It then counter - attacked the Chinese , taking Seoul again , and driving the communist forces back above the 38th parallel into North Korea . Next , the front stabilized in the 38th parallel area . When General Ridgway replaced General of the Army Douglas MacArthur as the overall U . N . commander , Lieutenant General James Van Fleet assumed command of Eighth Army . After the war of movement during the first stages , the fighting in Korea settled down to a war of attrition . Ceasefire negotiations were begun at the village of Panmunjom in the summer of 1951 , and they dragged on for two years . When the Military Demarcation Line was finally agreed to by the , the Eighth Army had succeeded in its mission of liberating South Korea , but the realities of a limited war in a world of nuclear weapons had become obvious . South Korea and North Korea continued on as separate states . Post Korean War . During the aftermath of the Korean War , the Eighth Army remained in South Korea , but the forces under its command were continually reduced as the demands of the U . S . Army in Europe and then the Vietnam War increased . By the 1960s , only the I Corps , consisting of the 7th Infantry Division and the 2nd Infantry Division , remained as part of the Eighth Army . Then , in 1971 , further reductions occurred . The 7th Infantry Division was withdrawn from South Korea , along with the command units of I Corps , which were moved across the Pacific Ocean to Ft . Lewis , Washington , leaving only the 2nd Infantry Division to watch the Korean Demilitarized Zone and to assist the South Korean Army in defending South Korea . Besides forming a trip - wire against another North Korean invasion , the 2nd Infantry Division remained there as the only " Army " unit in South Korea armed with tactical nuclear weapon s . ( Otherwise , there is only the U . S . Air Force in South Korea and on Okinawa . ) All nuclear weapons were taken from the Army to be under Air Force control . Later , all U . S . nuclear weapons were removed from South Korea . An occasional armed clash aside , relations between the two Koreas remained as stable as could be expected . By the end of the Cold War , the American army and Air Force in South Korea were regarded as a trip - wire force , not so much deployed for their military use but for their political value . An attack on South Korea by North Korea would mean an attack on the U . S . Army as well . However , in 2003 , plans were announced to move almost all of the 2nd Infantry Division ( Eighth Army ) southwards , away from the border . That would in turn reduce its " trip wire " effect . This provoked a heated debate in South Korea , where the future of the Eighth Army is still a contentious topic . The Headquarters of the Eighth Army is located at Yongsan Garrison , but it is scheduled to move southward to Camp Humphreys by 2019 . Current structure . Current structure . Eighth Army , Yongsan Garrison