Question: Which two forces have come to the aid of South Korea during The Korean War and, especially, The Battle of Pyongyang?

full_context: Document 1: Korean War: The Korean War (in South Korean Hangul: 한국전쟁 ; Hanja: 韓國戰爭 ; RR: "Hanguk Jeonjaeng " , "Korean War"; in North Korean Chosŏn'gŭl: 조국해방전쟁 ; Hancha: 祖國解放戰爭 ; MR: "Choguk haebang chǒnjaeng " , "Fatherland Liberation War"; 25 June 1950 – 27 July 1953) was a war between North Korea (with the support of China and the Soviet Union) and South Korea (with the principal support of the United States). The war began on 25 June 1950 when North Korea invaded South Korea. The United Nations, with the United States as the principal force, came to the aid of South Korea. China came to the aid of North Korea, and the Soviet Union also gave some assistance to the North.
Document 2: United States in the Korean War: At the conclusion of World War II the Allied nations began the process of disarmament of Axis controlled regions. Japan occupied Korea at this time and had been in control since 1910. In 1945, the decision was made to have American Marines forces oversee Japanese surrender and disarmament south of the 38th parallel and the Soviet Union would facilitate the change of power to the north. At the time there was no political motivation and seemed to be a logical and convenient plan of action. The original agreement and intent was to create a unified and independent Korea out of the post Japanese occupation era. Instead each side of the 38th parallel established its own government under the influence of the occupational country; the United States in South Korea and the Soviet Union in North Korea. Both new Korean governments discredited the other and claimed to be the only legitimate political system. Tensions between the North and South escalated and each side began to petition foreign powers for resources and support. South Korea wanted weapons and supplies from Truman and the United States government while North Korea sought help from Stalin and the Soviet Union. The United States was still war weary from the disruptive World War II campaign and refused South Korea's request for weapons and troops. North Korea convinced the Soviet Union to supply them with the weapons and support they requested. This decision coincided with the United States withdrawing the last remaining combat troops from South Korea. North Korea saw its opportunity and attacked South Korean forces at the 38th parallel on June 25, 1950 and thus initiating the Korean War.
Document 3: South Korea–United States relations: Republic of Korea–United States relations (Hangul: 한미 관계 ; Hanja: 韓美 關係 ; RR: "Hanmi gwangye "; MR: "Hanmi kwan'gye " ) have been extensive since 1950, when the United States helped establish the modern state of South Korea, also known as the Republic of Korea, and fought on its UN-sponsored side in the Korean War (1950–1953). During the subsequent four decades, South Korea experienced tremendous economic, political and military growth, and significantly reduced U.S. dependency. From Roh Tae-woo's administration to Roh Moo-hyun's administration, South Korea sought to establish an American partnership, which has made the Seoul–Washington relationship subject to some strains, especially with the Anti-US/Korean sentiments. However, relations between the United States and South Korea have greatly strengthened under the conservative, pro-U.S. Lee Myung-bak administration. At the 2009 G-20 London Summit, U.S. President Barack Obama called South Korea "one of America's closest allies and greatest friends." In addition, South Korea has been designated as a Major non-NATO ally.
Document 4: Battle of Pusan Perimeter: The Battle of Pusan Perimeter was a large-scale battle between United Nations and North Korean forces lasting from August 4 to September 18, 1950. It was one of the first major engagements of the Korean War. An army of 140,000 UN troops, having been pushed to the brink of defeat, were rallied to make a final stand against the invading North Korean army, 98,000 men strong.
Document 5: Battle of P'ohang-dong: The Battle of P'ohang-dong was an engagement between the United Nations and North Korean forces early in the Korean War, with fighting continuing from 5–20 August 1950 around the town of P'ohang-dong, South Korea. It was a part of the Battle of Pusan Perimeter, and was one of several large engagements fought simultaneously. The battle ended in a victory for the United Nations after their forces were able to drive off an attempted offensive by three North Korean divisions in the mountainous eastern coast of the country.
Document 6: Battle of Taegu: The Battle of Taegu was an engagement between UN and North Korean forces early in the Korean War, with fighting continuing from August 5–20, 1950 around the city of Taegu, South Korea. It was a part of the Battle of Pusan Perimeter, and was one of several large engagements fought simultaneously. The battle ended in a victory for the United Nations after their forces were able to drive off an offensive by North Korean divisions attempting to cross the Naktong River and assault the city.
Document 7: Korean War National Museum: The Korean War National Museum (KWNM) is a private-sector non-profit Illinois-based corporation headquartered in Springfield, Illinois. The KWNM seeks to create a museum and educational program to help people understand American participation in the Korean War (1950-1953), especially from the point of view of the men and women who served in combat and support roles. Founded in 1997, the KWNM reorganized in 2010 with the goal of expanding itself and building an accredited museum facility in New York City. A 10,000 square foot KWNM facility, the Denis J. Healy Freedom Center, currently operates in Springfield, Illinois. Open Tuesday-Saturday 10AM-5PM.
Document 8: Battle of Pyongyang (1950): The Battle of Pyongyang (17–19 October 1950) was one of the major battles of the United Nations and South Korean offensive during the Korean War. Following the Battle of Inchon, the UN forces recaptured Seoul, the capital of South Korea, and proceeded to north of the 38th parallel. Shortly after advancing north, the American and South Korean forces faced the North Korean defensive near Pyongyang, the capital of North Korea, on October 17. Since North Korea's leadership and its main forces had already withdrawn to Kanggye, the allied forces soon captured Pyongyang on October 19.The battle was followed by an airborne assault by the U.S. 187th Infantry Regiment 40km north of Pyongyang, with the intention of cutting off North Korean units retreating from the city.
Document 9: Battle of Pusan Perimeter logistics: Logistics in the Battle of Pusan Perimeter (August 4 – September 15, 1950) during the Korean War played a decisive role in the battle. Efficient logistics, the management of personnel and materiel, supported United Nations (UN) supply lines while the North Koreans' routes of supply were steadily reduced and cut off. UN logistics improved throughout the Battle of Inchon and the defeat of the North Korean army at Pusan.
Document 10: Battle of Inchon: The Battle of Inchon () was an amphibious invasion and battle of the Korean War that resulted in a decisive victory and strategic reversal in favor of the United Nations. The operation involved some 75,000 troops and 261 naval vessels, and led to the recapture of the South Korean capital of Seoul two weeks later. The code name for the operation was Operation Chromite.
Document 11: Third Battle of Seoul: The Third Battle of Seoul, also known as the Chinese New Year's Offensive, the January–Fourth Retreat (Korean: 1•4 후퇴 ) or the Third Phase Campaign Western Sector (), was a battle of the Korean War, which took place from December 31, 1950 to January 7, 1951 around the South Korean capital of Seoul. In the aftermath of the major Chinese victory at the Battle of the Ch'ongch'on River, the United Nations Command started to contemplate the possibility of evacuation from the Korean Peninsula. Upon learning of this development, China's Chairman Mao Zedong ordered the Chinese People's Volunteer Army to cross the 38th parallel in an effort to pressure the United Nations forces to withdraw from South Korea.
Document 12: Second Phase Campaign: The Second Phase Campaign of the Korean War was an extended military offensive by the Chinese People's Volunteer Army during the last week of November, 1950, and the first two weeks of December. The two major engagements were battles near the Ch'ongch'on River in the Chinese-designated Western Sector and Chosin Reservoir in their Eastern Sector. The Chinese opposed United Nations-authorized forces composed of American military and various allied forces.
Document 13: Foreign relations of North Korea: The foreign relations of North Korea – officially the Democratic People's Republic of Korea (DPRK) – have been shaped by its conflict with capitalist countries like South Korea and its historical ties with world communism. Both the government of the DPRK and the government of South Korea (officially the Republic of Korea) claim to be the government of the whole of Korea. The Korean War in the 1950s failed to resolve the issue, leaving the DPRK locked in a military confrontation with South Korea and the United States Forces Korea across the Demilitarized Zone. At the start of the Cold War, the DPRK only had diplomatic recognition by Communist countries. Over the following decades, it established relations with developing countries and joined the Non-Aligned Movement. When the Eastern Bloc collapsed in the years 1989–1991, the DPRK made efforts to improve its diplomatic relations with developed capitalist countries. At the same time there were international efforts to resolve the confrontation on the Korean peninsula, especially when the North acquired nuclear weapons after the demise of the Soviet Union, its main economic backer.
Document 14: Korean War POWs detained in North Korea: Tens of thousands of South Korean soldiers were captured by the North Korean and Chinese forces during the Korean War (1950–53) but were not returned during the prisoner exchanges under the 1953 . Most are presumed dead, but the South Korean government estimates some 560 South Korean prisoners of war still survive in North Korea. The issue of unaccounted South Korean POWs from the Korean War has been in dispute since the Armistice in 1953. North Korea continues to deny it holds these South Korean POWs. Interest in this issue has been renewed since 1994, when Lt. Cho Chang-ho, a former South Korean soldier presumed to have been killed in the war, escaped from North Korea. As of 2008, 79 former South Korean soldiers have escaped from North Korea.
Document 15: Battle of Yongju: The Battle of Yongju (21–22 October 1950), also known as the Battle of the Apple Orchard, took place as part of the United Nations (UN) offensive towards the Yalu River, against the North Korean forces which had invaded South Korea during the Korean War. The battle was fought between the 27th British Commonwealth Brigade and the North Korean 239th Regiment which was encircled east of Yongju, where it was attacking the US 187th Airborne Regimental Combat Team (US 187 RCT). On 20 October US 187 RCT had parachuted ahead of the advancing UN spearheads into drop zones in Sukchon and Sunchon, 40 km north of the capital Pyongyang, with the objectives of cutting off the retreating North Korean forces that were withdrawing up the west coast of the Korean Peninsula and releasing American and South Korean prisoners of war. Although the airborne drop itself was a success, the operation came too late to intercept any significant North Korean elements and the American landings initially met little resistance. However, on 21 October as US 187 RCT began to advance south to the clear the Sukchon to Yongju road towards Pyongyang the Americans came under heavy attack from the North Korean 239th Regiment, and requested assistance.
ground_truth: The United Nations, with the United States as the principal force