Folks tuning in to watch I Love the Seventies a few minutes early the last few weeks will have seen one or all of the following: a black and white photograph of a shed full of executed peasant women; a line drawing recreating the image of a ditch the size of a field being filled with 10,000 dead bodies; film of a small stocky man with a moustache being cheered by half a million of his countryfolk as he led them to war; and the gates of a concentration camp, glinting in the afternoon sunlight. BBC2 have just finished repeating their BAFTA award winning 1997 documentary series on the rise and fall of Nazi Germany, but sequenced it ineptly between fond evocations of the ’70s and repeats of classic comedies from the archives. Sure, an inspired alternative to the Saturday night fodder on the other channels between 8pm and 9pm, but why such a bizarre and awkward timeslot, nestling between fun tributes to the past that rely on laughs and loving nostalgia?

It’s the second time this series has been re-shown in almost as many years, but unlike most fare that comes in for the Beeb rapid repeat treatment, it’s wholly deserving of its multiple showings. It remains to my mind perhaps the best historical documentary series, along with The Cold War, the BBC have made during at least the last five years. This final episode examined the issue: why did Hitler continue with the war past the point when it was obvious Germany was going to lose?

The programme was the kind you had to be in the right frame of mind to watch – I had to video it and view it away from its Saturday night timeslot so I could properly enjoy and appreciate I Love 1975. Using primary source material – film, photos, letters, papers, sound recordings and objects – interspersed with calm narration and interviews with people in the present day recalling the events in question, the episode moved steadily, wearily, through the terrible tale of the last two years of World War II. It was all here: atrocity upon atrocity; betrayal; corruption; desperation, heartache, extermination.

Hitler had decreed that the war should be one “of annihilation”; Germany had to fight to the end because the only way to secure an early peace was to remove Hitler, but he had made himself irremovable, untouchable, irreplaceable. He alone had the power to end hostilities; he refused, believing that Germany should never surrender, and so there should be a fight to the end. The programme dealt mainly with what this meant for the whole of Europe, Germany included. When an assassination attempt on Hitler failed, German citizens rejoiced – “When I was told about the attack on Hitler, I was outraged,” recalled a member of the Hitler Youth. “I was totally outraged that something like this could happen. There was widespread relief that the attack had failed.” A member of Hitler’s German staff also spoke of how he would’ve reacted had he learnt of the plot. “I would have said to (the plotter) that I’m going to report to Hitler that you want to kill him. Yes. I had no other choice. If I had stayed quiet they would have put me in the little notebook and I would be shot.”

There’s still something compelling and unsettling about hearing Hitler speak. Silent black and white newsreels, for all their visual power, seem somehow less frightening, immediate, offensive than actual audio archives. Some radio broadcasts were played during the programme, and it was impossible not to be captivated in some ghastly way at how instead of the mechanical whiny tone that would befit his stature and caricature, Hitler’s voice was strangely deep, resonant and rounded.

When you are shown footage of Nazi propaganda films in television histories such as these – grotesque shots of almost clone-like figures frolicking in fields – they always seem to have been shot in lurid bright colour; whereas film of Auschwitz, or of the bombed city of Dresden, or the Jewish ghettos in Poland, is always, has always to be, in grim black and white. Colour doesn’t belong in a place like Auschwitz, it would almost be tasteless to see shots of that nightmarish place in anything other than monochrome. Strange how history becomes fixed in the memory according to trivial issues such as whether something was filmed on this or that camera.

The level of research that went into this series was astonishing. Not only had countless rare and archive footage been assembled, but the people in that original footage had been tracked down and interviewed today. It was fascinating watching how they rationalised their behaviour both at the time when ruled by a Nazi state, and in retrospect from the present day. One person admitted to being a “madman”, almost as if he had become someone else for the duration of the Hitler’s reign, but was now back to his old, true, real self. Also, seeing how the German people – the innocent victims of Nazi rule – had to behave while under Hitler’s command, being told to continue believing in victory even as the Russians bombarded the outskirts of Berlin, being shot if they dared mutter a word of criticism in Nazi earshot, was mesmerising.

Learning of the destruction of Dresden by the RAF – “Churchill’s murder boys” as one German remembered calling them – which together with the bombing of other German cities killed 350,000 civilians during the last 15 months of the war (three times more than in the previous three years put together) still shocks; no-one was innocent in this war, everyone committed obscene atrocities, it was just a question of who could rationalise them the quickest, easiest and most efficiently. “It was sadistic,” recalled a former SS soldier today, “Some officers liked sadistic things. They liked it when the mothers and children were screaming. They were really hot for that. In my view, these people were not human.”

Hitler ended up portrayed as a pathetic ridiculous figure. By 1945 he was, in the words of one of his old General Staff employees, “a very sick man, with a severe shaking paralysis in his right arm, a shuffling gait, blue glasses; he had poor eyesight so everything had to be written in large letters. But he had lost none of his demonic charisma. He was convinced – and I heard him say it – that after the end of him and of national socialism, the German people could not survive, it was destined to collapse. That was mentally sick.”

One of the most worrying images appeared right at the end of the film: a photo of Hitler wrapped up in a huge army trenchcoat peering through the rubble of Berlin, looking utterly isolated and alone, with just one solitary guard for protection; so different from almost all the other footage and images of Hitler which show him proud and fit and surrounded by adoring acolytes. This was a Hitler – most terrifyingly of all – appearing to be almost human. Shortly after the photo was taken, he shot himself.

Of all the images of World War II, the ones that remain the most overwhelming, most affecting and emotional, are always those showing the concentration camps. It is impossible to ever concisely describe how you feel seeing pictures of crates of skeletal naked bodies, or huge mounds of corpses piled up like a giant haystack – these images never lose their significance and resonance, no matter how many times they are shown. The programme let such images speak for themselves, with just one comment – how Hitler’s greatest legacy was “new knowledge of what human beings are capable of.”

World War II remains visually, through film and photos from the time, the most significant event of the last 100 years. No other time generated such a canon of images that retain their power to provoke reaction, horror, and confusion time and again. As a moment in history, the War seems to also hold the key to so many contemporary debates and issues – why there is so much significance in, for instance, joining the Euro, so-called “illegal” immigrants entering the country, what it means when you see a Union Jack, why there is a two minute silence on 11 November, and why there’s a swastika sprayed on a wall just down the street from where I live that never gets washed off.

If any event from 20th century history is deserving of more treatment through documentary television then World War II probably has to be it. Any programme that demonstrates the care, attention, intelligence and imagination shown by the team behind The Nazis: A Warning From History, led by producer/writer (and Timewatch editor) Laurence Rees, shows just why no channel perhaps in the world beats the BBC when making factual TV.

This series’ most enduring, ultimate concern was to ensure the viewer understood the Nazis rise and fall as, what the title stated, “a warning from history” – in that the way in which Hitler rose to power and conducted himself should be recalled and seen as significant for today’s society. This was in essence a re-statement of the fundamental purpose of all television history programmes, from those for schools to those for any age: to make their subject relevant to today. It is an enduring and laudable commitment. As if to reinforce just such an ideal, the series ended with a quotation from a German born philosopher, Karl Jaspers, writing just after the War had finished:

“That which has happened is a warning. To forget it is guilt. It was possible for this to happen, and it remains possible for it to happen again at any minute.”