When we think of Nazi evil, we think of Auschwitz: the deadliest Nazi camp and the deadliest Holocaust site. But there was more to the history of the camps and the Holocaust than Auschwitz.

The SS operated over 25 concentration camps during the Nazi dictatorship (1933–45), and over 1,100 attached satellite camps. These camps did not all operate at the same time, however. The SS system changed all the time, and so did the prisoner population, the conditions and the buildings. There was no typical concentration camp.

The history of the camps begins in 1933, seven years before Auschwitz was even set up. In the wake of the Great Depression, German democracy (the Weimar Republic) was destroyed. Its place was taken by the Nazi dictatorship, led by Adolf Hitler. Although the Nazi party had lots of popular support – it gained almost 44 per cent of the vote in the last multiparty elections in March 1933 – millions of Germans still rejected it.

The new rulers brutally attacked real and imagined opponents. Many victims were taken to early camps. In 1933, most inmates were political prisoners, above all German Communists. Many faced abuse and violence. Deaths were still rare, however, and most prisoners were released after a few weeks or months. Fear of the camps helped to break the anti-Nazi resistance. As a result, fewer opponents ended up inside, and by October 1934 only 2,400 prisoners were left in concentration camps. Some observers thought the camps would disappear completely.

But Adolf Hitler wanted to keep the camps: he saw the benefits of lawless terror, without courts and judges. And so Hitler supported the creation of a permanent concentration camp system under SS leader Heinrich Himmler. When war broke out in autumn 1939, after the German invasion of Poland, this SS system included six purpose-built camps holding 21,400 prisoners.

During the Second World War, concentration camps spread through much of Nazi-occupied Europe. Auschwitz, set up in 1940 to crush the Polish resistance, was the first of many new camps. Conditions inside camps, always poor, now became deadly. Many inmates died from illness and starvation. Many more were executed or died during horrific medical experiments.

From 1942, the camps participated in the Holocaust. Most of the six million European Jews murdered by the Nazis died outside concentration camps, shot or gassed on the killing fields of eastern Europe. Still, the single most lethal site of the Holocaust was a concentration camp: Auschwitz. Here, the SS killed some one million Jews; most were murdered on arrival in gas chambers.

In Auschwitz and other concentration camps, prisoner numbers grew fast during the second half of the war. Those regarded as fit for work by the SS (Jews and non-Jews alike) were used as slave labourers. Prisoners toiled for many hours each day, building roads, digging tunnels, breaking rocks, and more. Inmate numbers reached over 700,000 in early 1945. By then, the SS held most prisoners in satellite camps, which had sprung up near factories and building sites.

The end came in the first months of 1945, when Allied troops conquered what was left of the Third Reich. But liberation came too late for many concentration camp inmates. Between January and May 1945 (when Germany capitulated), an estimated 300,000 prisoners died. Victims of disease, starvation and execution, they died inside the hellish compounds and on death marches away from abandoned camps.

Overall, some 2.3 million men, women and children were taken to concentration camps between 1933 and 1945. Their fate was shaped by many factors, such as age, gender and nationality. There were many different prisoner groups, including Jews, political prisoners (from Germany and abroad), homosexuals, criminals, Gypsies, Soviet POWs and Jehovah’s Witnesses. They all experienced the camps differently. Inmate relations were often tense, but there was also much comradeship and resistance.

The SS ruled the concentration camps with an iron fist. It enforced brutal rules and rigid schedules. But just as there was no typical camp and no typical prisoner, there was no typical perpetrator either. By no means all men and women in the Camp SS were depraved murderers. But most of them quickly got used to the abuse of prisoners and upheld SS terror to the end.

Liberation was no happy end. Most prisoners had died before the Allies arrived. And the camps left a bitter legacy for survivors. They suffered from injuries and haunting memories, while most perpetrators got away unpunished. Meanwhile, ordinary Germans often pleaded ignorance. They did not know about the SS crimes, they said. This was one of many lies about the camps. After all, the camps had been public knowledge during the Third Reich. To combat such lies, and to learn lessons from the camps, we need to understand their complex history.