The Battle of Pakchon (5 November 1950), also known as the Battle of Bochuan (Chinese: ; pinyin: B Chun Zhn Du), took place ten days after the start of the Chinese First Phase Offensive, following the entry of the Chinese People's Volunteer Army (PVA) into the Korean War. The offensive reversed the United Nations Command (UN) advance towards the Yalu River which had occurred after their intervention in the wake of the North Korean invasion of South Korea at the start of the war. The battle was fought between British and Australian forces from the 27th British Commonwealth Brigade with American armour and artillery in support, and the PVA 117th Division of the 39th Army, around the village of Pakchon on the Taeryong River. After capturing Chongju on 30 October the British and Australians had been ordered to pull back to Pakchon in an attempt to consolidate the western flank of the US Eighth Army. Meanwhile, immediately following their success at Unsan against the Americans, the PVA 117th Division had attacked southward, intending to cut off the UN forces as they withdrew in the face of the unexpected PVA assault. To halt the PVA advance, the 27th British Commonwealth Brigade was ordered to defend the lower crossings of the Taeryong and Chongchon rivers as part of a rearguard, in conjunction with the US 24th Infantry Division further upstream on the right.

During the night of 4/5 November, the PVA and Korean People's Army (KPA) mounted a full-scale assault on the US 24th Infantry Division, pushing back an American infantry regiment nearly 2 kilometres (1.2 mi). The PVA/KPA force subsequently turned west, advancing between the Taeryong and Chongchon rivers and threatening the rear of the 27th British Commonwealth Brigade by cutting the PakchonSinanju road. The following day they attacked an American artillery battery which was guarding a vital concrete bridge near Kujin. The British and Australians then successfully counter-attacked the PVA forces occupying a number of nearby ridgelines during the day but were in turn counter-attacked before being pushed off the high ground during the night. In their first battle with the PVA, the 3rd Battalion, Royal Australian Regiment (3 RAR) captured a well defended hill with only limited offensive support, and held it in the face of heavy counter-attacks before confused command decisions resulted in a disorganised night withdrawal while still in contact. The withdrawal threatened to open the 27th British Commonwealth Brigade's left flank and the Australians were ordered to immediately reposition on the ridge, yet ultimately it was too late to regain the feature in darkness. However, following heavy fighting the pressure on the Australians unexpectedly ceased after midnight, and parties of PVA were observed beginning to withdraw. By early morning the PVA attack had been checked and 3 RAR had redeployed to new positions in the paddy fields around the railway crossing north of Maenjung-dong.

The fighting was costly for both sides. Although the Australians halted the advancing PVA 117th Division and inflicted numerous casualties on them, they also suffered heavy losses. In the aftermath the inexperienced Australian battalion commanderLieutenant Colonel Floyd Walshwas relieved of his position by the British brigade commander, having taken over just six days earlier following the death of the previous commanding officer Lieutenant Colonel Charles Green at Chongju. Nonetheless, the 27th British Commonwealth Brigade succeeded in preventing a PVA break-through at Pakchon, keeping open vital withdrawal routes across the river and securing the UN left flank. Suffering significant casualties, the PVA offensive was halted the next day due to logistic difficulties. The PVA and KPA were temporarily forced to withdraw north, while the UN successfully reinforced its positions, holding on the Chongchon Line. Yet by late November the US Eighth Army was again forced to withdraw after the PVA began their Second Phase Offensive, starting a long retreat south. The UN forces withdrew from North Korea to the 38th Parallel where they sought to re-establish defensive positions.

The Korean War (see § Names) was a war fought between North Korea and South Korea from 1950 to 1953. The war began on 25 June 1950 when North Korea invaded South Korea following clashes along the border and rebellions in South Korea. North Korea was supported by China and the Soviet Union while South Korea was supported by the United Nations, principally the United States. The fighting ended with an armistice on 27 July 1953.

In 1910, Imperial Japan annexed Korea, where it ruled for 35 years until its surrender at the end of World War II on 15 August 1945. The United States and the Soviet Union divided Korea along the 38th parallel into two zones of occupation. The Soviets administered the northern zone and the Americans administered the southern zone. In 1948, as a result of Cold War tensions, the occupation zones became two sovereign states. A socialist state, the Democratic People's Republic of Korea, was established in the north under the totalitarian communist leadership of Kim Il-sung while a capitalist state, the Republic of Korea, was established in the south under the authoritarian autocratic leadership of Syngman Rhee. Both governments of the two new Korean states claimed to be the sole legitimate government of all of Korea, and neither accepted the border as permanent.

North Korean military (Korean People's Army (KPA)) forces crossed the border and drove into South Korea on 25 June 1950. The United Nations Security Council denounced the North Korean move as an invasion and authorized the formation of the United Nations Command and the dispatch of forces to Korea to repel it. The Soviet Union was boycotting the UN for recognizing Taiwan (Republic of China) as China, and China (People's Republic of China) on the mainland was not recognized by the UN, so neither could support their ally North Korea at the Security Council meeting. Twenty-one countries of the United Nations eventually contributed to the UN force, with the United States providing around 90% of the military personnel.After the first two months of war, South Korean Army (ROKA) and American forces hastily dispatched to Korea were on the point of defeat, retreating to a small area behind a defensive line known as the Pusan Perimeter. In September 1950, a risky amphibious UN counteroffensive was launched at Incheon, cutting off KPA troops and supply lines in South Korea. Those who escaped envelopment and capture were forced back north. UN forces invaded North Korea in October 1950 and moved rapidly towards the Yalu River—the border with China—but on 19 October 1950, Chinese forces of the People's Volunteer Army (PVA) crossed the Yalu and entered the war. The UN retreated from North Korea after the First Phase Offensive and the Second Phase Offensive. Chinese forces were in South Korea by late December.

In these and subsequent battles, Seoul was captured four times, and communist forces were pushed back to positions around the 38th parallel, close to where the war had started. After this, the front stabilized, and the last two years were a war of attrition. The war in the air, however, was never a stalemate. North Korea was subject to a massive US bombing campaign. Jet fighters confronted each other in air-to-air combat for the first time in history, and Soviet pilots covertly flew in defense of their communist allies.

The fighting ended on 27 July 1953 when the Korean Armistice Agreement was signed. The agreement created the Korean Demilitarized Zone (DMZ) to separate North and South Korea, and allowed the return of prisoners. However, no peace treaty was ever signed, and the two Koreas are technically still at war, engaged in a frozen conflict. In April 2018, the leaders of North and South Korea met at the DMZ and agreed to work toward a treaty to formally end the Korean War.The Korean War was among the most destructive conflicts of the modern era, with approximately 3 million war fatalities and a larger proportional civilian death toll than World War II or the Vietnam War. It incurred the destruction of virtually all of Korea's major cities, thousands of massacres by both sides, including the mass killing of tens of thousands of suspected communists by the South Korean government, and the torture and starvation of prisoners of war by the North Koreans. North Korea became among the most heavily bombed countries in history. Additionally, several million North Koreans are estimated to have fled North Korea over the course of the war.