Imperial Japan destroyed the influence of China over Korea in the First Sino-Japanese War (1894–95), ushering in the short-lived Korean Empire.

Japan made Korea its protectorate with the Eulsa Treaty in 1905.

Many Korean nationalists fled the country. The Provisional Government of the Republic of Korea was founded in 1919 in Nationalist China.

At the Cairo Conference in November 1943, China, the United Kingdom and the United States all decided that "in due course Korea shall become free and independent".

Soviet Union declared war on Japan on 9 August 1945, three days after the USA atomic bombing of Hiroshima.

By 10 August, the Red Army had begun to occupy the northern part of the Korean Peninsula.

On the night of 10 August in Washington, US Colonels Dean Rusk and Charles H. Bonesteel III were assigned with dividing the Korean Peninsula into Soviet and US occupation zones and proposed the 38th Parallel.

On 8 September 1945, US Lieutenant General John R. Hodge arrived in Incheon to accept the Japanese surrender south of the 38th Parallel.

The Soviet Union withdrew as agreed from Korea in 1948, and US troops withdrew in 1949.

A general election was held in the South on 10 May 1948.

The resultant South Korean government promulgated a national political constitution on 17 July 1948, and elected Syngman Rhee as President on 20 July 1948.

The Republic of Korea (South Korea) was established on 15 August 1948.

North Korea held parliamentary elections three months later on 25 August.

In April 1950, Stalin gave Kim permission to invade the South under the condition that Mao would agree to send reinforcements if needed. Stalin made it clear that Soviet forces would not openly engage in combat, to avoid a direct war with the US.

Kim met with Mao in May 1950. Mao was concerned the US would intervene but agreed to support the North Korean invasion. China desperately needed the economic and military aid promised by the Soviets.

By June 1950, according to American intelligence, North Korean forces numbered 74,370 Korean Peoples' Army troops and 20,000 in the Border Constabulary, organized into 10 infantry divisions, one tank division, and one air force division, with 210 fighter planes and 280 tanks, who captured scheduled objectives and territory, among them Kaesong, Chuncheon, Uijeongbu, and Ongjin.

On 7 June 1950, Kim Il-sung called for a Korea-wide election on 5–8 August 1950 and a consultative conference in Haeju on 15–17 June 1950.

On 11 June, the North sent three diplomats to the South as a peace overture that Rhee rejected outright.

On 21 June, Kim Il-Sung revised his war plan to involve a general attack across the 38th Parallel, rather than a limited operation in the Ongjin Peninsula. Kim was concerned that South Korean agents had learned about the plans and that South Korean forces were strengthening their defenses. Stalin agreed to this change of plan.

The conflict escalated into warfare when North Korean military (KPA) forces—supported by the Soviet Union and China—crossed the border and advanced into South Korea on 25 June 1950.

On 25 June 1950, the United Nations Security Council unanimously condemned the North Korean invasion of South Korea, with UN Security Council Resolution 82.

On 27 June, Rhee evacuated from Seoul with some of the government.

On 27 June President Truman ordered US air and sea forces to help South Korea.

After debating the matter, the Security Council, on 27 June 1950, published Resolution 83 recommending member states provide military assistance to the Republic of Korea.

On 28 June, Rhee ordered the massacre of suspected political opponents in his own country.

On 28 June, at 2 am, the ROK (South) blew up the Hangang Bridge across the Han River in an attempt to stop the KPA (North).

On 4 July the Soviet Deputy Foreign Minister accused the US of starting armed intervention on behalf of South Korea.

The Battle of Osan, the first significant US 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 KPA at Osan but without weapons capable of destroying the KPA tanks. They were unsuccessful; the result was 180 dead, wounded, or taken prisoner.

Against the rested and re-armed Pusan Perimeter defenders and their reinforcements, the KPA were undermanned and poorly supplied; unlike the UN forces, they lacked naval and air support. To relieve the Pusan Perimeter, General MacArthur recommended an amphibious landing at Incheon, near Seoul and well over 160 km (100 mi) behind the KPA lines. On 6 July, he ordered Major General Hobart R. Gay, commander of the US 1st Cavalry Division, to plan the division's amphibious landing at Incheon.

After the first two months of war, the ill-equipped and underprepared South Korean Army (ROKA) and the US forces rapidly dispatched to Korea were on the point of defeat, forced back to a small area behind a defensive line known as the Pusan Perimeter.

On 4 August 1950, with a planned invasion of Taiwan aborted due to the heavy US naval presence, Mao reported to the Politburo that he would intervene in Korea when the People's Liberation Army's (PLA) Taiwan invasion force was reorganized into the PLA North East Frontier Force.

On 20 August 1950, Premier Zhou Enlai informed the UN that "Korea is China's neighbor ... The Chinese people cannot but be concerned about a solution of the Korean question". Thus, through neutral-country diplomats, China warned that in safeguarding Chinese national security, they would intervene against the UN Command in Korea.

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.

In September 1950, an amphibious UN counter-offensive was launched at Incheon, and cut off many KPA troops in South Korea.

By 15 September, the amphibious assault force faced few KPA defenders at Incheon: military intelligence, psychological warfare, guerrilla reconnaissance, and protracted bombardment facilitated a relatively light battle. However, the bombardment destroyed most of the city of Incheon.

On 16 September Eighth Army began its breakout from the Busan Perimeter. Task Force Lynch, 3rd Battalion, 7th Cavalry Regiment, and two 70th Tank Battalion units (Charlie Company and the Intelligence–Reconnaissance Platoon) advanced through 171.2 km (106.4 mi) of KPA territory to join the 7th Infantry Division at Osan on 27 September.

On 18 September, Stalin dispatched General H. M. Zakharov to North Korea to advise Kim Il-sung to halt his offensive around the Pusan perimeter and to redeploy his forces to defend Seoul.

On 25 September, Seoul was recaptured by UN forces. US air raids caused heavy damage to the KPA, destroying most of its tanks and much of its artillery. KPA troops in the south, instead of effectively withdrawing north, rapidly disintegrated, leaving Pyongyang vulnerable.

On 27 September, MacArthur received the top secret National Security Council Memorandum 81/1 from Truman reminding him that operations north of the 38th Parallel were authorized only if "at the time of such operation there was no entry into North Korea by major Soviet or Chinese Communist forces, no announcements of intended entry, nor a threat to counter our operations militarily".

On 27 September, Stalin convened an emergency session of the Politburo, in which he condemned the incompetence of the KPA command and held Soviet military advisers responsible for the defeat.

On 29 September MacArthur restored the government of the Republic of Korea under Syngman Rhee.

On 30 September, Zhou Enlai warned the US that China was prepared to intervene in Korea if the US crossed the 38th Parallel. Zhou attempted to advise KPA commanders on how to conduct a general withdrawal by using the same tactics that allowed Chinese communist forces to successfully escape Chiang Kai-shek's Encirclement Campaigns in the 1930s, but by some accounts KPA commanders did not use these tactics effectively.

By 1 October 1950, the UN Command repelled the KPA northwards past the 38th Parallel; the ROK advanced after them, into North Korea.

UN forces invaded North Korea in October 1950 and moved rapidly towards the Yalu River (the border with China).

During October, the South Korean police executed people who were suspected to be sympathetic to North Korea, and similar massacres were carried out until early 1951.

In a series of emergency meetings that lasted from 2 to 5 October, Chinese leaders debated whether to send Chinese troops into Korea.

MacArthur made a statement demanding the KPA's unconditional surrender. Six days later, on 7 October, with UN authorization, the UN Command forces followed the ROK forces northwards.

On 8 October 1950, Mao re designated the PLA North East Frontier Force as the People's Volunteer Army (PVA).

To enlist Stalin's support, Zhou and a Chinese delegation arrived in Moscow on 10 October, at which point they flew to Stalin's home on the Black Sea.

Meanwhile, on 15 October 1950, President Truman and General MacArthur met at Wake Island.

Immediately on his return to Beijing on 18 October 1950, Zhou met with Mao Zedong, Peng Dehuai and Gao Gang, and the group ordered two hundred thousand PVA troops to enter North Korea, which they did on 19 October.

The Eighth US Army drove up western Korea and captured Pyongyang on 19 October 1950.

On 19 October 1950, Chinese forces of the People's Volunteer Army (PVA) crossed the Yalu and entered the war. The surprise Chinese intervention triggered a retreat of UN forces back below the 38th Parallel by late December.

After secretly crossing the Yalu River on 19 October, the (People's Volunteer Army) PVA 13th Army Group launched the First Phase Offensive on 25 October, attacking the advancing UN forces near the Sino-Korean border.

The UN Corps landed at Wonsan (in southeastern North Korea) and Riwon (in northeastern North Korea) on 26 October, but these cities had already captured by ROK forces.

After inflicting heavy losses on the ROK II Corps at the Battle of Onjong, the first confrontation between Chinese and US military occurred on 1 November 1950.

On 13 November, Mao appointed Zhou Enlai the overall commander and coordinator of the war effort, with Peng as field commander.

On 24 November, the Home-by-Christmas Offensive was launched with the US Eighth Army advancing in northwest Korea, while US X Corps attacked along the Korean east coast.

On 25 November on 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 inflicted heavy losses on the US 2nd Infantry Division on the UN forces' right flank.

In the east on 27 November the PVA 9th Army Group initiated the Battle of Chosin Reservoir.

X Corps managed to establish a defensive perimeter at the port city of Hungnam on 11 December and were able to evacuate by 24 December in order to reinforce the badly depleted US Eighth Army to the south.

On 16 December 1950, President Truman declared a national state of emergency with Presidential Proclamation No. 2914, 3 C.F.R. 99 (1953). which remained in force until 14 September 1978.

The next day, 17 December 1950, Kim Il-sung was deprived of the right of command of KPA by China.

UN morale hit rock bottom when Lieutenant General Walton Walker, commander of the U.S. Eighth Army, was killed on 23 December 1950 in an automobile accident.

Lieutenant General Matthew Ridgway assuming the command of the US Eighth Army on 26 December.

the PVA and the KPA launched their Third Phase Offensive (also known as the "Chinese New Year's Offensive") on New Year's Eve of 1950/51.

The offensive overwhelmed UN forces, allowing the PVA and KPA to capture Seoul for the second time on 4 January 1951.

In late January, upon finding that the PVA had abandoned their battle lines, General Ridgway ordered a reconnaissance-in-force, which became Operation Thunderbolt (25 January 1951).

In mid-February, the PVA counterattacked with the Fourth Phase Offensive and achieved initial victory at Hoengseong. But the offensive was soon blunted by US IX Corps at Chipyong-ni in the center. The US 23rd Regimental Combat Team and the French Battalion fought a short but desperate battle that broke the attack's momentum. The battle is sometimes known as the "Gettysburg of the Korean War": 5,600 South Korean, U.S., and French troops were surrounded on all sides by 25,000 PVA. UN forces had previously retreated in the face of large PVA/KPA forces instead of getting cut off, but this time they stood and fought, and won.

Following the failure of ceasefire negotiations in January, the United Nations General Assembly passed Resolution 498 on 1 February, condemning the PRC as an aggressor, and called upon its forces to withdraw from Korea.

On 1 March 1951, Mao sent a cable to Stalin emphasizing the difficulties faced by Chinese forces and the need for air cover, especially over supply lines. Apparently impressed by the Chinese war effort, Stalin agreed to supply two air force divisions, three anti-aircraft divisions, and six thousand trucks.

On 7 March 1951, the Eighth Army attacked with Operation Ripper, expelling the PVA and the KPA from Seoul on 14 March 1951.

Operation Courageous was a military operation performed by the United Nations Command (UN) during the Korean War designed to trap large numbers of Chinese People's Volunteer Army (PVA) and Korean People's Army (KPA) troops between the Han and Imjin Rivers north of Seoul, opposite the Republic of Korea Army (ROK) I Corps. The intent of Operation Courageous was for US I Corps, which was composed of the US 25th and 3rd Infantry Divisions and the ROK 1st Infantry Division, to advance quickly on the PVA/KPA forces and reach the Imjin River with all possible speed.

Operation Tomahawk was an airborne military operation by the 187th Regimental Combat Team (187th RCT) on 23 March 1951 at Munsan-ni as part of Operation Courageous in the Korean War. Operation Courageous was designed to trap large numbers of Chinese People's Volunteer Army (PVA) and Korean People's Army (KPA) forces between the Han and Imjin Rivers north of Seoul, opposite the Republic of Korea Army (ROK) I Corps. The intent of Operation Courageous was for US I Corps, which was composed of the US 25th and 3rd Infantry Divisions and the ROK 1st Division, to advance quickly on the PVA/KPA positions and reach the Imjin River with all possible speed.

On 11 April 1951, President Truman relieved the General MacArthur as Supreme Commander in Korea. There were several reasons for the dismissal. MacArthur crossed the 38th Parallel in the mistaken belief that the Chinese would not enter the war, leading to major allied losses. He believed that whether to use nuclear weapons should be his decision, not the President's.

MacArthur was the subject of congressional hearings in May and June 1951, which determined that he had defied the orders of the President and thus had violated the US Constitution.

For the remainder of the war the UN and the PVA/KPA fought but exchanged little territory, as the stalemate held. Large-scale bombing of North Korea continued, and protracted armistice negotiations began on 10 July 1951 at Kaesong, an ancient capital of North Korea located in PVA/KPA held territory.

The Battle of the Punchbowl, was one of the last battles of the movement phase of the Korean War. Following the breakdown of armistice negotiations in August 1951, the United Nations Command (UN) decided to launch a limited offensive in the late summer/early autumn to shorten and straighten sections of their lines, acquire better defensive terrain, and deny the enemy key vantage points from which they could observe and target UN positions. The Battle of Bloody Ridge took place west of the Punchbowl from August–September 1951 and this was followed by the Battle of Heartbreak Ridge northwest of the Punchbowl from September–October 1951. At the end of the UN offensive in October 1951, UN forces controlled the line of hills north of the Punchbowl.

The Battle of Bloody Ridge was a ground combat battle that took place during the Korean War from 18 August to 5 September 1951. By the summer of 1951, the Korean War had reached a stalemate as peace negotiations began at Kaesong. The opposing armies faced each other across a line which ran from east to west, through the middle of the Korean peninsula, located in hills a few miles north of the 38th Parallel in the central Korean mountain range. United Nation and the North Korean Korean People's Army (KPA) and Chinese People's Volunteer Army (PVA) forces jockeyed for position along this line, clashing in several relatively small but intense and bloody battles. Bloody Ridge began as an attempt by UN forces to seize a ridge of hills which they believed were being used as observation posts to call in artillery fire on a UN supply road.

The Battle of Heartbreak Ridge , also known as the Battle of Wendengli , was a month-long battle in the Korean War which took place between 13 September and 15 October 1951. After withdrawing from Bloody Ridge, the Korean People's Army (KPA) set up new positions just 1,500 yards (1,400 m) away on a 7-mile (11 km) long hill mass. If anything, the defenses were even more formidable here than on Bloody Ridge. The Battle of Heartbreak Ridge was one of several major engagements in the hills of North Korea a few miles north of the 38th Parallel (the pre-war boundary between North and South Korea), near Chorwon. For the Chinese, this battle is often confused with the Battle of Triangle Hill, which occurred a year later.

On 24 February 1952, the Military Commission, presided over by Zhou, discussed the PVA's logistical problems with members of various government agencies involved in the war effort.

The Battle of Hill Eerie refers to several Korean War engagements between the United Nations Command (UN) forces and the Chinese People's Volunteer Army (PVA) in 1952 at Hill Eerie, a military outpost about 10 miles (16 km) west of Ch'orwon. It was taken several times by both sides; each sabotaging the others' position.

The Battle of Old Baldy refers to a series of five engagements for Hill 266 in west-central Korea. They occurred over a period of 10 months in 1952–1953, though there was also vicious fighting both before and after these engagements. UN victory in 1952 action Chinese victory in 1953 action

The Battle of White Horse, was a battle during the Korean War hill in the Iron Triangle, formed by Pyonggang at its peak and Gimhwa-eup and Cheorwon-eup at its base, a strategic transportation route in the central region of the Korean peninsula.

The Battle of Triangle Hill, also known as Operation Showdown or the Shangganling Campaign, was a protracted military engagement during the Korean War. The main combatants were two United Nations (UN) infantry divisions, with additional support from the United States Air Force, against elements of the Chinese People's Volunteer Army (PVA) 15th and 12th Corps. The battle was part of UN attempts to gain control of "The Iron Triangle", and took place from 14 October to 25 November 1952.

In 1952, the US elected a new president, and on 29 November 1952, the president-elect, Dwight D. Eisenhower, went to Korea to learn what might end the Korean War.

The Battle of Pork Chop Hill comprises a pair of related Korean War infantry battles during April and July of 1953. These were fought while the United Nations Command (UN) and the Chinese and North Koreans negotiated the Korean Armistice Agreement. In the U.S., they were controversial because of the many soldiers killed for terrain of no strategic or tactical value, although the Chinese lost many times the number of US soldiers killed and wounded. The first battle was described in the eponymous history Pork Chop Hill: The American Fighting Man in Action, Korea, Spring 1953, by S.L.A. Marshall, from which the film Pork Chop Hill was drawn. The UN won the first battle but the Chinese won the second battle.

The Battle of Kumsong, also known as the Jincheng Campaign , was one of the last battles of the Korean War. During the ceasefire negotiations seeking to end the Korean War, the United Nations Command (UNC) and Chinese and North Korean forces were unable to agree on the issue of prisoner repatriation. South Korean President Syngman Rhee, who refused to sign the armistice, released 27,000 North Korean prisoners who refused repatriation. This action caused an outrage among the Chinese and North Korean commands and threatened to derail the ongoing negotiations. As a result, the Chinese decided to launch an offensive aimed at the Kumsong salient. This would be the last large-scale Chinese offensive of the war, scoring a victory over the UNC forces.

Outpost Harry was a remote Korean War outpost located on a tiny hilltop in what was commonly referred to as the "Iron Triangle" on the Korean Peninsula. This was an area approximately 60 miles (100 km) northeast of Seoul and was the most direct route to the South Korean capital.

the KPA, the PVA and the UN Command signed the Korean Armistice Agreement on 27 July 1953.

After a new wave of UN sanctions, on 11 March 2013, North Korea claimed that the armistice had become invalid.

On 13 March 2013, North Korea confirmed it ended the 1953 Armistice and declared North Korea "is not restrained by the North-South declaration on non-aggression".

On 30 March 2013, North Korea stated that it entered a "state of war" with South Korea and declared that "The long-standing situation of the Korean peninsula being neither at peace nor at war is finally over".

Speaking on 4 April 2013, the US Secretary of Defense, Chuck Hagel, informed the press that Pyongyang "formally informed" the Pentagon that it "ratified" the potential use of a nuclear weapon against South Korea, Japan and the United States of America, including Guam and Hawaii.

On 27 April 2018, it was announced that North Korea and South Korea agreed to talks to end the ongoing 65-year conflict. They committed themselves to the complete denuclearization of the Korean Peninsula.