The United States military mounted an amphibious invasion of Korea at the port of Inchon on September 15, 1950. The invasion was part of a wider offensive during the first year of the Korean War, in which the U.S., South Korean, and UN forces looked to break out from the small area of South Korea around the port of Pusan, in which their forces had been trapped by the advancing North Korean armies. General MacArthur, the commanding general of the U.S. and UN forces decided that an amphibious landing of U.S. troops was needed in order to split North Korean forces along two fronts and to start an offensive to retake the South Korean capital, Seoul.
The Inchon Invasion shifts the balance of power
The attack of Inchon (now spelled Incheon), a port city less than 50 kilometers from Seoul, took the North Korean forces largely by surprise, with the Americans making rapid advances and taking the city by September 19. The invasion flipped the balance of power in the war, with the North Koreans suddenly needing to split their forces in order to try to defend Seoul. On the 16th of September the U.S. Eighth Army began its breakout from the Pusan Perimeter, linking up with the invasion force in the North of the country by the end of the month. This assault marked the beginning of a phase of U.S. and UN dominance in the war, which would only be ended by the entry of Chinese troops into the war in late October.