Daniel McLaughlin traces the evolution of the depraved mix of racial theory and scientific method that led to six million deaths
The Holocaust entered thousands of lives with a postman's light tap on the door. In Hungary and Greece, it came as a postcard from relatives, with entreaties to follow them quickly to a wonderful place in the north. In Germany, it arrived as a written order to tidy homes, pack some things and prepare for "resettlement". For Jewish women in Vienna, it came wrapped in a small parcel with the request: "To pay, 150 marks, for the cremation of your husband - ashes enclosed from Dachau."
The Third Reich excelled in bureaucracy as it excelled in killing, and fashioned a Europe-wide murder industry with a cold eye for efficiency.
Early in Hitler's campaign to annihilate the Jews, mass murder was a bloody business. Refined officers who loudly cherished the classics of German art and culture began to demur at placing bullets in Jewish bodies and shovelling them into mass graves. Gypsies, homosexuals and political prisoners proved no cleaner to kill.
It was not enough to open a special hospital department to deal with SS men whose minds had collapsed under the weight of their crimes. A system was required not only to make mass murder as impersonal as possible, but also to accelerate the obliteration of a race that was seen to be poisoning Germany's lifeblood, a parasite enfeebling its increasingly futile efforts against the Allies.
The alternative, according to the logic of Hitler and his deputies, was inevitable defeat by a Jewish-led cabal of capitalists and Slav communists, who would wreak hideous revenge on Germany's sons and daughters before enslaving them for centuries.
The shame and misery that engulfed Germany after the first World War would be repeated tenfold, and Aryan mastery over the globe would be postponed indefinitely, humanity's golden dawn obliterated by a dark Semitic cloud of racial and moral mediocrity.
"This is not the second World War. This is the great racial war. In the final analysis, it is about whether the German and Aryan prevails here, or whether the Jew rules the world, and that is what we are fighting for out there." So wrote Hermann Goering, the Gestapo chief whose vanity was almost as intense as his loathing for the Jews.
It was this self-proclaimed "last Renaissance man" and lover of archaic German hunting dress who had ordered the seizure of all Jewish property after the Kristallnacht pogrom of November 1938, an orgy of violence that prompted him to predict "a final reckoning with the Jews" should foreign powers dare to challenge Nazi expansion.
While feeding Hitler's appetite for acquiring territory from the hated Slavs, the push into eastern Europe and the Soviet Union also lumbered him with millions more Jews, whom Germany was already struggling to put to use making weapons, digging stone for bombastic building projects and in deadly labour camps such as Dachau.
When Reinhard Heydrich offered, at Wannsee in January 1942, to ensure that all Jews in German-controlled territory were worked to death or exterminated, it was nothing new to the attendant Nazi officers. Back in 1939, Hitler had vowed that a world war would bring about "the annihilation of the Jewish race in Europe". What Heydrich did was slide the Nazi killing machine into a higher gear.
Jews were violently evicted from most of the remaining city ghettos and fed into a vast system designed to sweep people hundreds or thousands of miles to their deaths, with as little fuss and expense as possible. Poland - sparsely populated and with a good rail network - was at the dark heart of Hitler's Final Solution for Europe's Jews.
The country played unwilling host to almost 6,000 prison camps of various sizes and regimes, including notorious names such as Treblinka, Belzec, Majdanek and Sobibor, where up to two million people, almost all of them Jews, perished.
Auschwitz - revelling grimly in the lie that welcomed its victims in iron letters: "Work Brings Freedom" - was the most deadly of the lot. Originally a prison camp for Poles and Soviets, the mass killing began in September 1941, when 850 inmates were crammed into a sealed room and blue pellets of Zyklon B - a gas used in low doses to kill insects and rats - were poured inside.
Auschwitz commandant Rudolf Höss recalled how "the gassing set my mind at rest, for the mass extermination of the Jews was to start soon, and I was not certain as to how these mass killings would be carried out. Now we had the gas, and we had established a procedure".
The camp, near Krakow, was extended to neighbouring Birkenau in 1942, where a complex of gas chambers and crematoria was built to deal with the thousands of new prisoners who arrived in filthy cattle-trucks from across eastern Europe every day.
"No one will get out of here alive," the guards told Alfons Walkiewicz when, as a captured 18-year old fighter from the Polish resistance, his packed wagon clanked into Auschwitz in October 1942.
"The Germans warned us when we arrived: in this place, no one will hold out for more than 100 days," Walkiewicz recalls. "All our personal belongings were taken from us. We had to strip naked, keeping only our belts to hold up our trousers.
"They shaved us, not only our heads but also under the arms and the genital region. Then they dunked us in disinfectant, gave us a cold shower, and only then was I given a pair of trousers, a jacket and a striped cap, and shoes with wooden soles.
"We stopped being human beings. I became a number - 73,526."
Perhaps 1.5 million people had an Auschwitz number crudely tattooed on to their wrists. Few survived to show their scar to the outside world.
The pace of killing, at all the extermination camps, quickened as the war rolled on, and US involvement and the Soviet counter-attack turned the tide against Germany.
Some survived the relentless "selections" that spared those who were still strong enough to work, but most of the women, children and elderly were taken immediately from their train wagon to the gas chambers, and kept docile by the promise of a shower, food and rest. Anyone heard to warn new arrivals of their fate was hurled alive into the crematorium. The Nazis liked their enemies to die quickly, cleanly and quietly.
A few people, such as Sophia Litwinska, survived to tell the tale of the gas chamber:
"There were towels hanging round, and sprays, even mirrors. People were in tears; people were shouting at each other; people were hitting each other. Suddenly I saw fumes coming in through a very small window at the top.
"I had to cough violently, tears streaming from my eyes, and I had a sort of feeling in my throat as if I would be asphyxiated."
Litwinska was dragged unconscious from the chamber and, when relating her story after the war, still seemed unsure why she had been spared. Not many were so fortunate as the Final Solution gained momentum.
Dr Charles Bendel, a Romanian Jewish doctor, was ordered to work at the Auschwitz crematorium in August 1944. By then, the ovens were not able to burn bodies quickly enough to keep up with the efficiency of the gas chambers, which could kill 2,000 people at a time. So a set of canals was dug in the earth nearby, "through which the human fat or grease should seep so that the work could be continued in a quicker way," Dr Bendel recalled.
"The capacity of these trenches was almost fantastic. Crematorium number four was able to burn 1,000 people during the day, but this system of trenches was able to deal with the same number in one hour."
Dr Bendel worked with Dr Josef Mengele, the notorious Nazi doctor who experimented on scores of Auschwitz inmates before killing them with a lethal injection. His involvement at the camp, and that of medical colleagues at several others, belied the macabre scientific interest the Nazis took in their "sub-Aryan" victims.
The gas chambers of the Polish extermination camps were descended from the shower rooms in the extermination centres set up around Germany in the late 1930s, where some 70,000 mentally and physically handicapped people were executed. There, carbon monoxide rather than Zyklon-B was the preferred poison. This "euthanasia" project, T4, tempered a hard core of scientists and killers for the later work of exterminating the Jews.
Hitler argued that modern society was dulling the effects of natural selection by keeping alive the handicapped and the elderly, and so wasting resources that could be devoted to strong, healthy - and above all, Aryan - citizens.
In economically depressed post-war Germany, the Nazis portrayed the elimination of the sick, the elderly and the Jews - as well as "anti-social elements" such as the gypsies - as a quick way to cut welfare costs and allow a hike in military spending. Empty hospital beds were also needed for the war-wounded, while Jewish forced labour freed up German men to join the military, and their empty houses were snapped up by Germans "repatriated" from eastern Europe.
The Nazis co-opted economic ideas and twisted evolutionary theories to create a hatefully poisonous ideology of race, mingling extreme prejudice and expedience to seduce a nation that was poor, demoralised and hungry for a scapegoat for its suffering.
"They [the Jews] had to be treated like a tuberculosis bacillus, with which a healthy body may become infected," Hitler told Hungary's wavering wartime leader in 1943. "This was not cruel, if one remembers that even innocent creatures, such as hares and deer, have to be killed, so that no harm is caused by them. Why should the beasts who wanted to bring us Bolshevism be spared more? Nations that did not rid themselves of Jews perished."
As the Allies got the upper hand, Hitler began to fear that Hungary could go over to their side, and ordered the immediate occupation of the country in March 1944. Despite the efforts of Raoul Wallenberg and Carl Lutz, Swedish and Swiss diplomats who issued thousands of life-saving visas to Budapest's Jews, more than 400,000 of them were deported to Auschwitz. Before being killed, they were forced to sign postcards urging their relatives to quickly join them in lovely "Waldsee".
The Red Army arrived at the camp on January 27th, 1945. The SS had already abandoned the place where more than a million people had been murdered. The Final Solution had come up short - about five million of Europe's 11 million Jews escaped its maw.
"Among the inmates, you could not distinguish the men from the women, the young from the old. They were wide-eyed human beings with translucent skin," recalls Genry Koptev, now aged 80, who was part of the Soviet 322nd division that liberated the camp. "They were laughing and crying all at once, and telling us about their lives in all possible languages. Then I saw a whole alley bordered with two-metre high bonfires, from which human bodies emerged. The alley was leading to the camp's crematorium.
"I also saw a room where human hair was stockpiled, and another where there were only spectacles. Then I went into the shower room, whose walls were covered in dark blue tiles. But only after the Nuremberg trial did I learn how they were used. I could never understand how a human mind could conceive of this."
Neither, quite, could Primo Levi, the Italian chemist and writer who was one of the few men to walk away from Auschwitz. In If This is a Man, Levi's account of the year he spent in the camp, he recalls being perused by a curious Nazi doctor:
"If I had known how completely to explain the nature of that look, which came as if across the glass window of an aquarium between two beings who live in different worlds, I would also have explained the essence of the great insanity of the third Germany."