The world displays an enduring fascination for the second world war and the Vietnam war. Yet the 1950-53 Korean conflict, which killed up to 2m Koreans, several hundred thousand Chinese, together with 37,000 American, British and other United Nations soldiers, remains almost unknown, save through the film and television comedy M*A*S*H.

In Korea, for three years the cold war became hot. The battles of Chosin Reservoir, Pork Chop Hill, the Hook and Imjin river were as fierce as any of modern times. So why our indifference? Korea was an ugly, unglamorous struggle that nobody wanted to fight, in a faraway country hated by foreigners who fought there through its roasting summers and icy winters. Researching my own book about the war,more than 20 years ago, I met a British veteran who described how, amid the barren mountains, he received a bitter letter from his wife. Her neighbours thought he had left her. They were oblivious of his war.

David Halberstam was one of America's most respected journalists. He made his name in Vietnam, and became the author of a string of bestsellers. He was killed in a car crash last April, just after completing this book. It is a remarkable piece of storytelling, about the first 10 months of the Korean saga.

In 1945, after 35 years as a Japanese colony, the country was arbitrarily partitioned at the 38th parallel by the victors of the second world war. The Americans took responsibility for the south, the Russians for the north. The two superpowers adopted local client regimes, each of which rivalled the other in nastiness, and aspired to conquer its neighbour. The Americans, however, denied South Korea tanks and jets, while the Soviets provided the north with the means for aggression.

For years, western left-wing mythology held that the south was responsible for the outbreak of war in 1950. A Channel 4 series reasserted this nonsensical claim as late as 1987. But the end of the cold war enabled researchers to access Soviet and even some Chinese archives. One of many merits of Halberstam's book is that, thanks to this material, his book chronicles the exchanges between Moscow, Peking and Pyongyang. He details much that I and other historians assumed 20 years ago, but could not prove.

Stalin sanctioned the North Korean assault because he believed the Americans would not intervene and wished to strengthen his influence in the region at Mao Tse-tung's expense. The communists nearly succeeded. The invasion that began on June 25, 1950 swept through the South Korean territory of President Syngman Rhee, driving back the first ragtag American units that were rushed to Korea from Japan. By a hair's-breadth, America (with a small British contingent) held a perimeter around the port of Pusan. Then came one of the most dramatic moments of the war. In September, General Douglas MacArthur, 70 years old and effective emperor of Japan as well as Supreme Commander in Korea, launched a surprise amphibious assault on the western port of Inchon, far behind the communist front. His troops recaptured Seoul and drove premier Kim Il Sung's forces in a headlong rout back into the north - and onward to the Chinese border.

Halberstam is a wonderfully assured portraitist. His depiction of MacArthur the megalomaniac, perceiving a chance to reverse the 1948 “loss” of China to the communists, is superb. MacArthur could not and would not acknowledge that he was fighting a limited war, which neither superpower wished to widen. He wanted victory, of the kind America had achieved over Japan in 1945. Neither the politicians nor the generals back in Washington felt able to stop him. Mao did, however. While Stalin was too cautious to commit Soviet troops, Beijing warned the Americans through an Indian diplomat that it would not tolerate an American army on its border. When MacArthur kept marching north, Mao secretly dispatched into Korea a Chinese force that was eventually 300,000 strong. On the night of November 25, bugle-blowing Chinese troops swept down from the mountains upon Americans celebrating what seemed an easy victory.

The American army suffered one of the most humiliating defeats in its history. In “the big bug-out”, its broken units were driven back 120 miles in 10 days, losing most of their weapons and equipment. They were confounded by Chinese tactics. The communists fought at night when American air power was ineffective, racing across country to cut off road-bound American columns. Halberstam quotes one of the ablest American officers in Korea, Colonel Paul Freeman, who said: “Without air and artillery [the Chinese] are making us look a little silly in this godawful country.”

It was a frightening time. MacArthur, in his madness, declared that he “prayed on his knees” for Chinese intervention, to enable him to challenge communist power in Asia. Amid the shock of defeat, he blustered that he had been betrayed by Washington politicians. He wanted to accept Chiang Kai-shek's offer of Chinese nationalist troops for Korea - and hankered to use nuclear weapons. Mao dismissed the Bomb as “a paper tiger...China has millions of people. The deaths of 10m to 20m people is nothing to be afraid of”.

But western governments were appalled by fears that MacArthur might get to test Mao's resolve. It came as a huge relief around the world, when, in April 1951, President Truman dismissed MacArthur, replacing him with General Matthew Ridgway, whose brief was to play for a draw, not a victory, in Korea. Two more years of hard fighting, suffering and negotiation were required before this was achieved.

Halberstam's account of the winter battles is exemplary, especially his description of the “death ride” through the pass at Kunuri, where a whole American division was shattered. He also tells well the story of the one redeeming performance of that first campaign - the fighting retreat of US Marines from the Chosin Reservoir.

Some readers may be irked by the fact that the book is exclusively American in focus. The British, who played a significant marginal role, don't feature at all. This is a finely crafted story, with a wealth of anecdotage about American soldiers and politicians - notably Truman and secretary of state Dean Acheson. Time magazine, whose proprietor Henry Luce was a passionate foe of Truman and fan of MacArthur, declared that “seldom has a more unpopular man fired a more popular man”. Acheson, one of the most brilliant public servants in American history, became a hate figure for his supposed feebleness towards the communists. One day in Washington, as he climbed into a cab, the driver said: “You're Dean Acheson, aren't you.” The secretary of state demanded wryly: “Do you want me to get out?”

In truth, Truman and Acheson handled Korea as well as could be done. They repulsed communist aggression, without provoking a wider war. Posterity understands, as many contemporary Americans did not, that MacArthur was a dangerous egomaniac, whose misjudgments almost precipitated a catastrophe.

Because Halberstam's story stops in the spring of 1951, more than two years before an armistice was finally signed, it feels incomplete. He explains the cut-off: “The war had settled into unbearable, unwinnable battle; it had reached the point where there were no more victories, only death.” This is a fine narrative, within the author's chosen compass.

Those such as the British reporter James Cameron, who denounced Rhee's regime and UN support for it back in 1950, were wrong. Everything is relative. Rhee's rule was fractionally less ghastly than that of Kim Il Sung. Vindication for what the West did in that barren peninsula almost 60 years ago is to be found in the two Koreas today: one a thriving democracy and economic tiger; the other, one of the most wretched tyrannies on earth. Unlike most conflicts, the Korean war was worth fighting. This is Halberstam's conclusion, and most people reading his tale will understand why.

The Coldest Winter by David Halberstam
Macmillan £25 pp733

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