When we ask why the Sixties happened – the riots, the drugs, nuns marrying monks – one of the answers is Vietnam. The war in south-east Asia was such a colossal mistake built on so hideous a lie that it shattered the West’s claim to moral authority. It weakened respect for the US presidency, elders and betters, the military, capitalism, democracy, even God. So awful is Vietnam that it’s hard to imagine an objective documentary being made about it. The Vietnam War: a Film by Ken Burns and Lynn Novick (showing intermittently on BBC Four) very nearly pulls it off. It’s well researched, beautifully constructed and captivating. It’s also heart-breaking. In 1965, the Crocker family made a film to be sent to Private Denton Crocker Jr to wish him Merry Christmas, and we see a recording of a mom, dad, brother and sisters – full of gee-whiz innocence – wishing their boy good luck. Denton was attached to a battalion run by a man who offered a case of whiskey to the first soldier who brought him the severed head of an enemy soldier. The contest was won. Fighting a war with no fixed line, where territory was hard to conquer and much less easy to hold, victory was measured in the number of Vietnamese killed. The Americans cleared villages and dropped bombs; yet nothing could stop the insurgency. Denton was killed in action on June 4, 1966. It was a day after his 19th birthday. Footage of the early, fawning media coverage of the war speaks for itself; it’s plain to see that the generals lied to the cameras. President Lyndon Johnson knew that the war was unwinnable by the tactics he chose to fight it, yet kept going for fear that retreat would be a strategic catastrophe. But even though Burns and Novick acknowledge American guilt, I still found the use of a folksy Americana soundtrack irritating: the whole damn point is that this war was being fought in Asia, not on the fields of Tennessee. And even an 18-hour documentary cannot capture the cruel legacy of French imperialism, the cynicism of Kennedy and Johnson, the utter stupidity of Congress or the way that war ripped through American society like a bullet. Vietnam remains too big to film.