In 1950, as the international community was coming to terms with the aftermath of World War II, a new conflict broke out at the edge of the Asian continent.
It was a rare example of the Cold War turning hot - pitting the US and its allies against the USSR, North Korea and communist China. It was marked by dramatic swings of fortune and a devastating death toll.
Estimates vary, but at least two million Korean civilians, up to 1.5m communist forces, and around 30,000 US, 400,000 South Korean and 1,000 UK troops are believed to have died.
The suffering caused by the war continues to this day
For two of the three years that the war was under way, both sides were actually trying to negotiate a peace.
When a ceasefire was eventually signed, on 27 July 1953, no-one could have guessed that 50 years later, the two Koreas would remain technically at war.
A peace treaty has never been signed, and the border continues to bristle with mines, artillery and hundreds of troops.
North Korea Attacks
The Korean War was rooted in the country's complex recent history.
China, Japan and the Soviet Union had all jostled for influence over the Korean peninsula for years, before Japan's victory in the 1904-5 Russo-Japanese war made it the dominant power. Japan went on to formally colonise Korea in 1910 and ruled it until the end of World War II.
North Korea's bigger army initially had the upper hand
Just seven days before Japan's surrender at the end of that war, the Soviet Union took advantage of the changing fortunes and entered Korea. The USSR and the US later agreed to divide Korea at the 38th parallel, with the USSR in charge north of this line, and the US given jurisdiction over the south.
The Soviet Union established a communist dictatorship in the North under the leadership of Kim Il-sung, a former guerrilla leader who went on to surround himself in a cult of personality.
The US meanwhile held elections in the South and a President, Syngman Rhee, was chosen. Both occupying forces withdrew from Korea by 1949.
The USSR left behind a well-equipped and -trained North Korean army. It had at its disposal 135,000 men, supported by tanks and artillery.
The South's forces, by comparison, numbered only 98,000 and were effectively a constabulary force. This was partly because the US was anxious to deprive the South of the means to invade the North.
Both sides wanted a reunification of the peninsula - the North dreamed of a wholly communist peninsula, and the South of a unified democracy.
The North was encouraged by its superior military balance, and an ill-advised statement in January 1950 by US Secretary of State Dean Acheson, which appeared to leave South Korea out of the US' military defence commitments.
In the early hours of 25 June 1950, when half of the South's troops were on leave for the weekend, North Korea launched a surprise, but well co-ordinated, attack across the 38th parallel.
US troops were hurriedly sent from bases in Japan. But they and their South Korean allies fared badly in the initial confrontation with the North.
Beating a hasty retreat, they managed to hold on to a small area surrounding the port city of Busan, in the peninsula's south-eastern corner, while the US called on the United Nations Security Council for support.
The UN held emergency meetings before sending help
The Security Council passed a resolution which called on all members to help repel the invasion. The motion was only passed because the Soviet delegate, who would have certainly vetoed it, was absent because he was boycotting Security Council meetings until China was admitted to the UN.
Fourteen UN nations - Australia, Belgium, Canada, Colombia, Ethiopia, France, Greece, the Netherlands, New Zealand, the Philippines, South Africa, Thailand, Turkey and the United Kingdom - agreed to help, committing a force of some 300,000. Most of the military support - 260,000 troops - was provided by the US, but the UK, Canada and Australia all made a substantial commitment.
While reinforcements were readied, it fell to the limited troops already in the country to hold on to the pocket of territory they still controlled. Ironically, they were helped by the fact that their defensive line was now so short - a perimeter of just 50 by 100 miles around Busan - that it was easier to defend.
North Korean's supply lines were also dangerously overstretched by their rapid advance.
It fell to the US Eighth Army commander, General Walton Walker, to rally the troops. He delivered a famous "Stand or Die" speech stressing that the force could no longer retreat.
The South Korean army and just four, ill-equipped US divisions managed to hold off the North's battalions for six weeks, but more US troops died in this battle than in any other operation during the war. They had bought time with blood.
While the North's army was buffeting the Busan enclave, the head of UN forces in the conflict, General Douglas MacArthur, prepared to reverse the course of the war.
On 15 September 1950 he launched a daring, sea-borne assault on the western port city of Inchon.
The goal of the Inchon landing, deep behind enemy lines, was to cut the North Koreans' supplies and communications and trap them between the troops landing in the western port and the Busan units.
The Inchon landing was a high risk strategy
On 15 October, on Wake Island in the Pacific, General MacArthur and President Truman met to discuss the future of the war.
MacArthur reportedly told Truman that he was confident of early success in the North Korean offensive, and that he no longer feared Chinese intervention.
Just 10 days later, the Chinese army, which had been secretly massing at the border, made its first attack on the allies. In the days that followed, the allies' headquarters received intelligence that Chinese forces were hidden in the North Korean mountains, but this was disregarded.
China's entry into the war caused further upheaval
The Chinese troops withdrew, and the allies interpreted these initial skirmishes as simply defensive. Undeterred, General MacArthur ordered a bold offensive on 24 November to push right up to the Yalu River, which marked the border between North Korea and north-east China.
He optimistically hoped this would finish the war and allow the troops "home by Christmas". But it was instead to mark yet another turning point in the conflict. The next day, about 180,000 Chinese "volunteers" attacked.
A shocked MacArthur told Washington: "We face an entirely new war."
He ordered a long and humiliating retreat - performed in sub-zero temperatures - which took the troops below the 38th parallel by the end of December.
As Chinese troops unleashed a renewed offensive, the allies were forced to withdraw south of Seoul in January 1951. Here, in the relatively open terrain of South Korea, the UN troops were better able to defend themselves. After a few more months of fighting, the front eventually stabilised in the area of the 38th parallel.
igh-risk strategyGeneral MacArthur's plan was risky because it meant braving unpredictable tides in a rocky port and scaling a 15-foot high seawall - only to face a fortified island in the harbour and a city that was occupied by strong North Korean forces. After preparatory bombardment, two battalions entered Inchon, beating down resistance but meeting no counter-attack.
At the same time, the US Eighth Army broke free of the Busan corner and started pushing North. The North Koreans panicked and started fleeing, and by 25 September, the allies had recaptured Seoul.
The allies could have stopped at the 38th parallel, since South Korea was now liberated. But President Truman wanted to unify Korea under a single, pro-Western government.
General MacArthur therefore ordered a pursuit of the communist troops across the border. But Truman, fearing a wider war, stressed that MacArthur should stay clear of China.
China wanted North Korea to act as a buffer state. Beijing warned that it would enter the war if the troops crossed into North Korea, but these warnings were ignored.
source:BBC
