While the North's army was buffeting the Busan enclave, the head of UN forces in the conflict, General Douglas MacArthur, prepared to reverse the course of the war.
On 15 September 1950 he launched a daring, sea-borne assault on the western port city of Inchon.
The goal of the Inchon landing, deep behind enemy lines, was to cut the North Koreans' supplies and communications and trap them between the troops landing in the western port and the Busan units.
General MacArthur's plan was risky because it meant braving unpredictable tides in a rocky port and scaling a 15-foot high seawall - only to face a fortified island in the harbour and a city that was occupied by strong North Korean forces. After preparatory bombardment, two battalions entered Inchon, beating down resistance but meeting no counter-attack.
At the same time, the US Eighth Army broke free of the Busan corner and started pushing North. The North Koreans panicked and started fleeing, and by 25 September, the allies had recaptured Seoul.
The allies could have stopped at the 38th parallel, since South Korea was now liberated. But President Truman wanted to unify Korea under a single, pro-Western government.
General MacArthur therefore ordered a pursuit of the communist troops across the border. But Truman, fearing a wider war, stressed that MacArthur should stay clear of China.
China wanted North Korea to act as a buffer state. Beijing warned that it would enter the war if the troops crossed into North Korea, but these warnings were ignored.