Question: When did the U.S. go to war with the country which was divided at the end of World War II?

full_context: Document 1: Korean War: The Korean War (in South Korean Hangul: 한국전쟁, Hanja: 韓國戰爭, Hanguk Jeonjaeng, "Korean War"; in North Korean Chosungul: 조국해방전쟁, Joguk Haebang Jeonjaeng, "Fatherland Liberation War"; 25 June 1950 – 27 July 1953)[a] was started when North Korea invaded South Korea. The United Nations, with United States as the principal force, came to aid of South Korea. China, along with assistance from Soviet Union, came to aid of North Korea. The war arose from the division of Korea at the end of World War II and from the global tensions of the Cold War that developed immediately afterwards.
Document 2: Korean War: In the resulting Battle of Pusan Perimeter (August–September 1950), the U.S. Army withstood KPA attacks meant to capture the city at the Naktong Bulge, P'ohang-dong, and Taegu. The United States Air Force (USAF) interrupted KPA logistics with 40 daily ground support sorties that destroyed 32 bridges, halting most daytime road and rail traffic. KPA forces were forced to hide in tunnels by day and move only at night. To deny matériel to the KPA, the USAF destroyed logistics depots, petroleum refineries, and harbors, while the U.S. Navy air forces attacked transport hubs. Consequently, the over-extended KPA could not be supplied throughout the south. On 27 August, 67th Fighter Squadron aircraft mistakenly attacked facilities in Chinese territory and the Soviet Union called the UN Security Council's attention to China's complaint about the incident. The US proposed that a commission of India and Sweden determine what the US should pay in compensation but the Soviets vetoed the US proposal.
Document 3: Korean War: After the Incheon landing, the 1st Cavalry Division began its northward advance from the Pusan Perimeter. "Task Force Lynch" (after Lieutenant Colonel James H. Lynch), 3rd Battalion, 7th Cavalry Regiment, and two 70th Tank Battalion units (Charlie Company and the Intelligence–Reconnaissance Platoon) effected the "Pusan Perimeter Breakout" through 106.4 miles (171.2 km) of enemy territory to join the 7th Infantry Division at Osan. The X Corps rapidly defeated the KPA defenders around Seoul, thus threatening to trap the main KPA force in Southern Korea.
Document 4: United States Army: During the Cold War, American troops and their allies fought Communist forces in Korea and Vietnam. The Korean War began in 1950, when the Soviets walked out of a U.N. Security meeting, removing their possible veto. Under a United Nations umbrella, hundreds of thousands of U.S. troops fought to prevent the takeover of South Korea by North Korea, and later, to invade the northern nation. After repeated advances and retreats by both sides, and the PRC People's Volunteer Army's entry into the war, the Korean Armistice Agreement returned the peninsula to the status quo in 1953.
Document 5: Korean War: On 25 November at the Korean western front, the PVA 13th Army Group attacked and overran the ROK II Corps at the Battle of the Ch'ongch'on River, and then decimated the US 2nd Infantry Division on the UN forces' right flank. The UN Command retreated; the U.S. Eighth Army's retreat (the longest in US Army history) was made possible because of the Turkish Brigade's successful, but very costly, rear-guard delaying action near Kunuri that slowed the PVA attack for two days (27–29 November). On 27 November at the Korean eastern front, a U.S. 7th Infantry Division Regimental Combat Team (3,000 soldiers) and the U.S. 1st Marine Division (12,000–15,000 marines) were unprepared for the PVA 9th Army Group's three-pronged encirclement tactics at the Battle of Chosin Reservoir, but they managed to escape under Air Force and X Corps support fire—albeit with some 15,000 collective casualties.
Document 6: Military history of the United States: The Korean War was a conflict between the United States and its United Nations allies and the communist powers under influence of the Soviet Union (also a UN member nation) and the People's Republic of China (which later also gained UN membership). The principal combatants were North and South Korea. Principal allies of South Korea included the United States, Canada, Australia, the United Kingdom, although many other nations sent troops under the aegis of the United Nations. Allies of North Korea included the People's Republic of China, which supplied military forces, and the Soviet Union, which supplied combat advisors and aircraft pilots, as well as arms, for the Chinese and North Korean troops.
Document 7: Korean War: Korea was ruled by Japan from 1910 until the closing days of World War II. In August 1945, the Soviet Union declared war on Japan and—by agreement with the United States—occupied Korea north of the 38th parallel. U.S. forces subsequently occupied the south and Japan surrendered. By 1948, two separate governments had been set up. Both governments claimed to be the legitimate government of Korea, and neither side accepted the border as permanent. The conflict escalated into open warfare when North Korean forces—supported by the Soviet Union and China—invaded South Korea on 25 June 1950. On that day, the United Nations Security Council recognized this North Korean act as invasion and called for an immediate ceasefire. On 27 June, the Security Council adopted S/RES/83: Complaint of aggression upon the Republic of Korea and decided the formation and dispatch of the UN Forces in Korea. Twenty-one countries of the United Nations eventually contributed to the defense of South Korea, with the United States providing 88% of the UN's military personnel.
Document 8: United States in the Korean War: The first battle the Americans entered in the Korean War was the Battle of Osan, where about four hundred strong landed in Pusan airport on the first of July. The American troops were sent off to Taejon the next morning where Major General John H. Church the head of U.S. field headquarters was confident in the US troop's strengths to push back the North Koreans. On July fifth the troops were finally put to the test when North Korean tanks crept towards Osan. The four hundred infantryman of the U.S. also called Task Force Smith opened fire on the North Koreans at 8: 16 am. Only four of the North Korean tanks were destroyed and twenty - nine kept moving forward breaking the US line. At the end of the battle only two more North Korean Tanks and two regiments of North Korean infantry were destroyed. The US had lost the battle, revealing that the mere sight of US troops would not reverse the military balance in Korea. By early August, the North Korean troops had pushed back the US and South Korean troops all the way to Naktong River, which is located about thirty miles from Pusan. The two weeks of fighting following this resulted in the most casualties of US troops than any other equivalent period of this war. However, during this time the US pushed supplies and personnel to Korea and by the end of July South Koreans and US troops outnumbered the North Koreans, although the North had pushed back the US and South by an amazing amount the North had suffered over fifty thousand casualties. Also because North Koreas supply lines were so lengthy and with the US in control of the water and air replenishing there losses were slow.
Document 9: Battle of Taejon: The Battle of Taejon (14–21 July 1950) was an early battle of the Korean War, between American and North Korean forces. Forces of the United States Army attempted to defend the headquarters of the 24th Infantry Division. The 24th Infantry Division was overwhelmed by numerically superior forces of the Korean People's Army (KPA) at the major city and transportation hub of Taejon. The 24th Infantry Division's regiments were already exhausted from the previous two weeks of delaying actions to stem the advance of the KPA.
Document 10: Korean War: The Battle of Osan, the first significant American engagement of the Korean War, involved the 540-soldier Task Force Smith, which was a small forward element of the 24th Infantry Division which had been flown in from Japan. On 5 July 1950, Task Force Smith attacked the North Koreans at Osan but without weapons capable of destroying the North Koreans' tanks. They were unsuccessful; the result was 180 dead, wounded, or taken prisoner. The KPA progressed southwards, pushing back the US force at Pyongtaek, Chonan, and Chochiwon, forcing the 24th Division's retreat to Taejeon, which the KPA captured in the Battle of Taejon; the 24th Division suffered 3,602 dead and wounded and 2,962 captured, including the Division's Commander, Major General William F. Dean.
Document 11: Korean War: Meanwhile, U.S. garrisons in Japan continually dispatched soldiers and matériel to reinforce defenders in the Pusan Perimeter. Tank battalions deployed to Korea directly from the U.S. mainland from the port of San Francisco to the port of Pusan, the largest Korean port. By late August, the Pusan Perimeter had some 500 medium tanks battle-ready. In early September 1950, ROK Army and UN Command forces outnumbered the KPA 180,000 to 100,000 soldiers. The UN forces, once prepared, counterattacked and broke out of the Pusan Perimeter.
Document 12: South Korea: On June 25, 1950, North Korea invaded South Korea, sparking the Korean War, the Cold War's first major conflict, which continued until 1953. At the time, the Soviet Union had boycotted the United Nations (UN), thus forfeiting their veto rights. This allowed the UN to intervene in a civil war when it became apparent that the superior North Korean forces would unify the entire country. The Soviet Union and China backed North Korea, with the later participation of millions of Chinese troops. After an ebb and flow that saw both sides almost pushed to the brink of extinction, and massive losses among Korean civilians in both the north and the south, the war eventually reached a stalemate. The 1953 armistice, never signed by South Korea, split the peninsula along the demilitarized zone near the original demarcation line. No peace treaty was ever signed, resulting in the two countries remaining technically at war. Over 1.2 million people died during the Korean War.
Document 13: United States in the Korean War: In response to North Korea's invasion into South Korea the United Nations convened to formulate a response. The U.N. demanded North Korea's immediate withdrawal and, when this was not met, United States Army General Douglas MacArthur was appointed supreme commander of U.N. forces. To halt the rapid progress of North Korean forces into the south Task Force Smith was deployed to the Korean front from Japan. Task Force Smith consisted of U.S. Army officers and regiments of the Army's 24th Infantry Division that were stationed in Japan as occupational forces. Unfortunately the 24th were under trained, poorly supplied, and outnumbered. The 24th offered very little resistance against the North Korean advance. American and South Korean troops were pushed south and in late July 1950 Task Force Smith was overrun in the city of Taejon. Troops from the Army's 25th Infantry Division were deployed to Taejon to establish a new line and pullout the decimated 24th I.D. This addition of combat troops did not stop the North Korean advance and both American and South Korean troops were pushed further south.
Document 14: 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 following a series of clashes along the border. 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 15: Korean War: Korea was ruled by Imperial Japan from 1910 until the closing days of World War II. In August 1945, the Soviet Union declared war on Imperial Japan, as a result of an agreement with the United States, and liberated Korea north of the 38th parallel. U.S. forces subsequently moved into the south. By 1948, as a product of the Cold War between the Soviet Union and the United States, Korea was split into two regions, with separate governments. Both claimed to be the legitimate government of all of Korea, and neither accepted the border as permanent. The conflict escalated into open warfare when North Korean forces -- supported by the Soviet Union and China -- moved into the south on 25 June 1950. On 27 June, the United Nations Security Council authorized the formation and dispatch of UN forces to Korea to repel what was recognized as a North Korean invasion. Twenty - one countries of the United Nations eventually contributed to the UN force, with the United States providing 88% of the UN's military personnel.
ground_truth: the Battle of Osan
sub_queries: What country was divided at the end of World War II? Answer: Korea
when did the us go to war with Korea Answer: the Battle of Osan