Korean War - Key Events
September 12, 1950
North Korean troops reach their farthest point of advance. Although thousands of UN troops have arrived to reinforce South Korea, months of fighting have reduced the area under their control to a 5,000-square-mile rectangle centered on the critical southeastern port of Pusan. By the time the North Korean invasion force reaches the “Pusan Perimeter,” its strength has been nearly cut in half and it is almost entirely lacking in armor.
These events are taken from the Encyclopedia Britannica