It Was allready a road of death in 1942 thousands of British, Indians and fellow travellers fled Rangoon, hounded by bandits, after the Japanese took Burma. It was a road of carnage in March 1944, as 15,000 men from the 31st Infantry Division of Japan's Imperial Army marched up it, bent on taking Kohima, the gateway to India, and then bearing down on the crucial allied supply centre at Dimapur. And it was a road of bones – unburied bodies piled high, carcasses stripped clean by animals – as the famished, exhausted remnants of this mighty invasion force staggered back to Burma and ultimate surrender.Most of the big battles of the www.guardian.co.uk/world/secondworldwar have been analysed to exhaustion. But the siege of Kohima, a sleepy little hill town on the peripheries of the Raj, a nowhere-in-particular place that nobody bothered to protect until it was almost too late, has been all but forgotten. This is an epic story of the unfamiliar, which begins with benevolent deputy district commissioners playing tennis, as young lady anthropologists from Roedean study native art nearby. It goes on to reveal the tennis court strewn with corpses, while one of the anthropologists, Ursula Graham Bower, leads a band of Naga fighters through the forests to harry the Japanese.These are not cartoon heroics, though. Fergal Keane operates masterfully on three levels, setting this, the last military stand of British empire, in a far wider campaign context (and confirming Bill Slim's reputation as the best wartime general the British had). He views much of the conflict through the eyes of those, on both sides, who fought until they dropped: their personal testimony – Japanese as well as British – is still vivid, compelling and terrifying. And he doesn't suffer the fools who made grave mistakes gladly.Burma 1942 wasn't Whitehall's or Churchill's finest hour. Rangoon's white rulers, wastrel and racist, were allowed to play on heedlessly while the threat of Japan's 15th Army grew. Nobody thought that Tokyo would strike. Everybody was wrong. Nobody thought, after Pearl Harbor changed every equation, that General Mutaguchi's troops would try to push into India through the steep, wild Naga hills. Wrong again. British and Indian forces which might have held the Kohima pass were not reinforced but pulled out at the last minute.Defending the town, the road and the hillsides above it was left to, at most, 1,500 men, a rag-tag force of signallers, sappers, mule-drivers and a few hardened infantry. This random compote of Indian army, British and mixed regiments had neither cohesion nor – in some cases – much enthusiasm for battle. When the Japanese attacked, some fought with extreme bravery, but others ran away.At least a few hundred men from the Royal West Kent regiment returned to shore up Kohima's defences. Then the Japanese, short of air cover, ammunition and – most crippling of all – food supplies, began to lose hundreds of men in despairing charges against the town (and across that tennis court). Though the casualties grew and grew, the West Kents and the 1st Assams dug in, fighting yard by yard in a way that made Slim, at his HQ far away, remember Flanders fields. And then, painfully slowly, more relief columns inched up the road from Dimapur, lifted the siege and began – with still more blood, still more desperation – to clear the Japanese troops from the hills.It's some of the smaller, emotional details of this account that strike hardest. The leeches accompanying every march, the lice that infect open wounds, the mud and guts, the almost berserk heroism as Corporal John Harman VC storms two Japanese machine gun nests, the count of the dead day after day on that damned tennis court. Keane catches both shrinking revulsion and astounding courage to brilliant effect because he so often puts people first, because he knows that this all-consuming encounter could only look in on itself as the battle crawled from trench to trench through days and weeks without sleep. There wasn't a wider world in Kohima then: just more broken bodies in the ad hoc hospital, more broken minds slipping away into the forests of the night.On the outside, conventional history still operates. British generals doze too long and react too slowly. Top brass play politics more assiduously than the politicians. Messages, when they get through, go unread or are lost. The Nagas, faithful followers of the Union flag and dogged foes of Nehru's pending hegemony, are ditched without compunction when it's all over (and are today consigned to still more freedom-fighting against Bangladesh). The Americans, not very keen on imperialism of any kind themselves, don't do special relations in this conflict.But perhaps Keane's most memorable insights come on the Japanese side of this account. General Sato, the commander of the 31st, doubted the strategy of his superior, Mutaguchi, and he was right. The Kohima assault was a folly that, inexorably, hastened the 15th Army's collapse in Burma. There was terrible sickness, appalling dysentery; there was a hunger that could never be appeased and a supply chain that could never be repaired. Mutaguchi sat at his lush command centre hundreds of miles distant, eating his fill, summoning geishas – and telling his emperor and superiors in Tokyo that all would be well, that Sato was just making difficulties.Some difficulties! Of the 15,000 who marched on Kohima, more than half never came home. The bones along the final road belonged to them. Those who did make it back to Rangoon were traumatised and weak. It was a defeat that made continuing Japanese resistance futile. It was the little war that should have ended the great war in the Far East. Yet still there was pride, inflexibility, loyalty, disbelief; and still there was Hiroshima.I found myself, on one or two pages towards the close, caught in a choking emotion. The evidence is meticulously gathered and the writing so powerful that it turns a book about a battle into a book about human beings, their existence, their end. Keane's Kohima is more than one episode among many, more even than an account of how two differing empires fell apart. It is a book about life in death.Fergal Keane is at the Guardian www.guardian.co.uk/books/guardian-hay-festival on Tuesday 1 June. Peter Preston's 51st State is published by Penguin.