The young Belgian SS doctor Hans Delmotte arrived in Auschwitz in September 1944. Soon he saw his first selection: hundreds of bewildered, famished Jews led from railway cars and directed toward either certain death or a temporary reprieve. Delmotte was told that, as an Auschwitz doctor, he was expected to preside over selections, inspecting Jews and pointing to left or right, death or life. Shocked by this news, Delmotte collapsed. The next day, still shaking, Delmotte stammered that as a doctor he was meant to serve life, not death: He would never make a selection. He insisted to the camp commandant that he either be transferred to the Eastern front or be gassed himself. Some weeks later, Delmotte calmed down and agreed to perform his duty at the selection ramp. In Auschwitz he spent his time at the Hygiene Institute, using inmates to experiment with typhus.Seventy years after the Allies liberated the camps, we still read about the Holocaust and the other Nazi crimes in part because we are afraid of becoming like Hans Demotte: We fear that we will start to think of monstrous actions as just the way of the world. Like Ivan Karamazov we want to remain in revolt, refusing to accept the torture of innocents. But our refusal has no effect on the fact that, within living memory, mass murder became both ordinary and necessary. To protest this fact is a futile gesture. Faced with the impossible reality of the Shoah, even our indignation becomes impossible.Decades later, we more than ever before recognize ourselves in the dark mirror of that terrible time. There is no other way to explain the flood of books and movies about the Nazi era, which stems not from an appetite for cheap sensational evil, but from the sneaking suspicion that, if we had been placed under such inhuman pressures, such unheard-of temptations, we would have learned something deeply unfortunate about ourselves. We strongly suspect that, had we been put in a concentration camp—let’s say as a kapo, a victim forced to play the role of perpetrator—we would have failed any moral test you could think of. We need to experiment with that failure. We want our wishful image of ourselves as morally upstanding to break down, in order to see who we really might be. Yes, we are the righteous Ivan Karamazov who rebels against the torture of children, but we are also the guilty Ivan who lets his father be murdered and who can’t bear to think he has anything in common with the murderer. Which, of course, he does.The way we pay attention to the Holocaust is a test for us. The Shoah has often been used to demonstrate the toughness, if not the triumph, of the human spirit. In this way it is unique among genocides, which normally inspire pessimism rather than uplift. We cling to those survivor testimonies that cherish the marks of humane feeling still left among prisoners, so we can avoid thinking about how much humanness they had lost. We admire some prisoners’ stoicism of unhope so that we can turn our eyes away from the desperate panic of the ones about to die. But we must remain alert to our impulse to turn the victims’ suffering into a useful fable. In this arena, picking illustrations for ideas about God, fate, and human nature is not allowed. We cannot let the camps become storehouses for moral examples, because so much of what happened there makes morality collapse.***Nikolaus Wachsmann’s new book KL: A History of the Nazi Concentration Camps delivers a comprehensive history of an unendurable subject. KL stands for Konzentrationslager: concentration camp. When we contemplate Nazi terror we think most of all about what became the central camp, Auschwitz. But most of us know little about the others: for instance, the subterranean hell of Dora, built near the end of the war, where prisoners dug tunnels for underground rocket production. “The air in the sleeping tunnels was unbearable,” Wachsmann writes, “a mix of sweat, urine, excrement, and rotting corpses.” And sleep was impossible anyway because of the deafening explosions: Prisoners worked around the clock in two shifts. By April 1944 at least a third of them had died.Wachsmann has absorbed an enormous amount of recent research on the KL. From this mountain of material he has crafted a fluent and gripping history. In the past few decades thousands of books and articles have been published on the camp system, especially in Germany. Wachsmann builds on recent accounts of the KL like the comprehensive one by the German historian Karin Orth. Two encyclopedias on the camps, in German and English, have lately appeared: The German one (edited by Wolfgang Benz and Barbara Distel) is over 4,000 pages long. A number of new survivor testimonies have also come out, like Edgar Kupfer’s vast Dachau diaries, published in 1997. Wachsmann integrates all this work in an accomplished manner. He mostly avoids philosophical and ethical controversy, sticking to the facts of history.Wachsmann omits from his history the death factories the Nazis built on Polish soil in late 1941 and 1942: Chelmno, Sobibor, Belzec, Treblinka. These were never work camps, but rather extermination centers for the Jews of Europe. They can be classed with the work of the Einsatzgrüppen who swept across conquered Soviet territory in these years and who murdered with bullets nearly half the Jews who were to die in the Holocaust.Wachsmann gives a step-by-step account of how the camps developed. The KL appeared on the scene with astonishing swiftness, just weeks after Hitler took over power in late February 1933. The Nazis originally used the KL against the German people, as a way to warn dissenters that the new order demanded total obedience. Dachau was the flagship of the early KLs, and it had the worst conditions. The Nazi staffers, exultant at the defeat of the left-wing militias they had battled in the streets during the waning years of Weimar, cudgeled political prisoners without mercy.Along with Dachau, the camps in the Emsland moors in Saxony, close to the Dutch border, were particularly horrifying. One prisoner, Ernst Heilmann, was beaten with table legs, buried alive, and then led on a chain like a dog by an SS man who made him bark and yell, “I am the Jewish Parliamentary deputy Heilmann from the SPD” (the Social Democratic Party). Heilmann was then mauled by guard dogs. Shunted for years from one camp to another—at Oranienburg he found himself covered head to toe in excrement—Heilmann finally died a broken man in the early months of the war.What Heilmann, along with many other prisoners from this early period, went through still horrifies us. But infinitely worse horrors were to come. The Nazi machine of mass murder could not have been envisioned in the mid 1930s. The camps of 1933, Wachsmann shows, were a far cry from what they would become during the war. Even after Heinrich Himmler took over the KL in June 1936 and expanded the camp system in 1938-39, the vast majority of prisoners survived. In some camps prisoners even had time to relax playing chess, listening to music, or celebrating religious holidays—including Jewish ones. The KL was not yet geared to working prisoners to death or murdering them en masse. That would come later, during the war. Even the “November Jews” arrested in the wake of Kristallnacht were mostly released within months.The SS, who ran the camps, singled out Jewish prisoners for especially violent abuse, but at times other groups were isolated just as harshly: politicals, “asocials” (criminals), gay men, Roma and Sinti, Jehovah’s Witnesses. Jews usually got the hardest work details. They were forced to curse themselves as “Jewish swine” while they labored in quarries. But the asocials, an increasing population in the late-1930s KL, also came in for rough treatment. We lack information on the criminal prisoners: Though most of them were petty thieves rather than violent thugs, they had a dark reputation in the camps. Political prisoners were praised as heroes after the war, especially in Communist East Germany. By contrast, Wachsmann notes, there is only one memoir by an asocial, and it came out in 2014.Faced with the impossible reality of the Shoah, even our indignation becomes impossible.Many camps were located in the middle of towns, and most Germans knew they existed. Tourists in Nuremberg castle could hear the screams of prisoners from the KL in the cellar. In the mid-1930s the Nazis actively publicized the camps. The chief targets, Germans were told, were (in Wachsmann’s words) “primarily Communist ‘terrorists,’ followed by SPD ‘fat cats’ and other ‘dangerous characters.’ ” Released prisoners spread the news about the tortures they had endured, though they often suppressed the worst details from fear of a second arrest. Camp guards boasted about their deeds in local bars.Not Jews but Soviet POWs were the first victims of annihilation in the KL. During the initial wild success of Operation Barbarossa Germany captured millions of Soviet soldiers. Most of them were starving to death in German POW camps deep in the newly seized Soviet territory when, in the fall of 1941, Himmler demanded hundreds of thousands of these new prisoners to serve as a work force for the Reich. Himmler got some of what he wanted: Thousands of prisoners were transported westward. But what happened to them in the KL was closer to mass extermination than forced labor. Few among the ten thousand Russians sent to Sachsenhausen in the fall of 1941 survived more than a few weeks in the camp.Many of the features we associate with the Shoah were first used on Soviet POWs in the camps. Doctors selected Russian soldiers to be sent to “showers,” where they were shot through the back of the neck—an innovation designed to spare the conscience of their killers, who could claim that they had not looked their victims in the eye. Gold teeth were pried from the mouths of the corpses. In Auschwitz Zyklon B was first used to kill Soviet “commissars”—in reality starving, bedraggled Russian infantrymen.The mass murder of Soviet POWS in the camps, Wachsman insists, was not a “dress rehearsal” for the Holocaust, because in 1941 Hitler had not come to the idea of annihilating all Jewish life in Europe. But it did provide a crucial precedent. In a late January 1942 lunch with Himmler, shortly after the Wannsee Conference that sealed the Jews’ fate, Hitler raved that Europe must become Judenfrei and added, “I see only one thing: total annihilation, if they don’t go voluntarily. Why should I look at a Jew with different eyes than a Russian prisoner?” Since Germany had now barred Jews from leaving Europe “voluntarily,” the only route left was murdering them, just as the Russians had been murdered. The KL, and above all Auschwitz, served this purpose in the last years of the war.From 1943 on Auschwitz became both the biggest wartime KL and the most prominent death factory—over 800,000 Jews were murdered at Birkenau within hours of their arrival, and less than 1 percent of Jewish children survived the initial selection for the gas chambers. The primary function of Auschwitz was to murder as many Jews as possible, though some 20 percent of those who arrived at the camp evaded immediate death. As a camp Auschwitz was “in a league of its own,” as Wachsmann remarks, and its name has become shorthand for the Holocaust itself. But there was also Majdanek, site of the largest slaughter of Jews in a single day in any KL (18,000, on Nov. 3, 1943), and the lethal labor camp Mauthausen.In his chapters on Auschwitz, Wachsmann revisits well-known territory. Like other historians, he weaves together powerful vignettes of individuals with a more general account of how the camp functioned. He is always eloquent, and his judgments are well-measured, but most of this material will be familiar to readers of earlier books about the camp. There are a few revelations, though. Wachsmann cites some important recent work on the Sonderkommando, the prisoners who had the hellish job of moving corpses from the gas chambers to the crematoria. We now know that the Sonderkommando were not routinely murdered en masse every three months, as some survivors and historians have claimed. There are smaller corrections, too: Hair harvested from the heads of doomed Jewish women was not used to make slippers for U-Boat men. Those tons of hair went largely unused, testimony to the senseless German need to convert their Jewish victims into mere material.Wachsmann’s discussion of the fate of children in the camps is the hardest to endure. Here we read about the special barrack in Majdanek for children and babies. The SS regularly emptied the barrack, sending the children to the gas chamber. “The children screamed and did not want to go,” the Majdanek survivor Henrika Mitron remembered. On the way to Auschwitz, Wachsmann writes, another child, “little Samuel Langfus sobbed inconsolably, screaming again and again: ‘I want to live!’ ” At Auschwitz, the Jewish prisoner doctor Olga Lengyel, whose own children had already died in the gas chambers, sometimes killed newborn babies so that their mothers would be spared death, instead of being murdered along with their infants. “And so, the Germans succeeded in making murderers of even us,” Lengyel wrote after the war. “To this day the picture of those murdered babies haunts me.” Cases like Lengyel’s remind us why the camps were so immensely cruel: They made the victims, not just the perpetrators, guilty of savage acts.Wachsmann aptly uses for the epigraph to his encyclopedic book a line from a letter by Salmen Gradowski buried in a flask in the Auschwitz-Birkenau crematorium and discovered after the war: “May the world at least behold a drop, a fraction of this tragic world in which we lived.” Were Wachsmann’s history 10 times as long as it is, it would still only give us a fraction, a mere drop, of what the Nazi regime’s victims suffered. And that, more than anything else, is why we should keep reading.***Like this article? Sign up for our Daily Digest to get Tablet Magazine’s new content in your inbox each morning.David Mikics is the author, most recently, of Bellow’s People: How Saul Bellow Made Life Into Art. He lives in Brooklyn and Houston, where he is John and Rebecca Moores Professor of English at the University of Houston.