Why did the Battle of Pusan occur?

Answer 1

By the time the Communist North Koreans attacked on June 25, 1950, there were only 200 U.S. "advisors" in South Korea. By the time the U.S. military landed reinforcements the South Koreans and the initial U.S. units had been pushed to the area around Pusan. In order to allow for adequate reinforcements to arrive, a perimeter was set up. On September 15, 1950, the 3rd Brigade Landing Team (BLT), 5th Marine Regiment, landed and took Wolmi-do near Inch'on, while the remainder of the 5th Marines and the 1st Marines assaulted other area objectives. On September 16, 1950 the Marine regiments had established a line on the east side of Inch'on and began to advance toward Seoul.

Near Pusan on 16 September the breakout began but with limited success. American Army Units with Republic of Korea Army units (ROKA) attacked and were counterattacked, gaining ground slowly until 22 September when the Battle of the Pusan Perimeter ended.

This breakout was important in that space was needed to gain momentum for maneuver warfare and to seize the initiative. Military forces cannot gain ground in a defensive role, and the priority was to retake lost South Korean cities and territory.