The Korean War (25 June 1950 – 27 July 1953) was an armed conflict on the Korean Peninsula fought between North Korea (Democratic People's Republic of Korea; DPRK) and South Korea (Republic of Korea; ROK) and their allies. North Korea was supported by the People's Republic of China and the Soviet Union, while South Korea was supported by the United Nations Command (UNC) led by the United States. Fighting ended in 1953 with an armistice, with no treaty signed.

After the end of World War II in 1945, Korea, which had been a Japanese colony for 35 years, was divided by the Soviet Union and US into two occupation zones at the 38th parallel, with plans for a future independent state. Due to political disagreements and influence from their backers, the zones formed their own governments in 1948. The DPRK was led by Kim Il Sung in Pyongyang, and the ROK by Syngman Rhee in Seoul; both claimed to be the sole legitimate government of all of Korea, and engaged in limited battles. On 25 June 1950, the Korean People's Army (KPA), equipped and trained by the Soviets, launched an invasion of the south. In the absence of the Soviet Union, the UN Security Council denounced the attack and recommended countries to repel the invasion. UN forces comprised 21 countries, with the US providing around 90% of military personnel.

After two months, the Republic of Korea Army (ROKA) and its allies were nearly defeated, holding onto only the Pusan Perimeter.