The 8th Army was officially activated on 10 June 1944. Under the command of Lieutenant General Robert L. Eichelberger, it became known as the "Amphibious Eighth" for its 60+ island assaults in the Pacific War, including in the Philippines, and was there being readied for the invasion of Japan when the war ended. The army then occupied Japan.
Walton H. Walker succeeded Eichelberger in 1948, and was in command when elements of the army entered Korea in June 1950, the army as a whole being active by 13 July of that year. It helped push the North Koreans beyond the 38th parallel, but was reversed when China joined the battle. Faced with a foe outnumbering them in the field by a huge margin, as well as overextended supply lines, Eighth Army fell back into South Korea.
Matthew Ridgway assumed command of the army upon Walker's death in an automobile accident in December 1950. Many historians give Ridgway credit with turning what had been a defeated, sullen force into a sharp, well-honed fighting force which ultimately overcame the numerical advantages the Chinese held, forcing Chinese Communist forces to negotiate an armistice.