Like most books about repressive regimes, “Hitler Youth” is laced with irony: The HJ (to use its standard German acronym), for instance, grew as quickly as it did because it got a leg up from the old German tradition of apolitical youth groups, which had primarily begun as individualist rebellions against “materialism and bourgeois complacency.” These proto-Youth were into Nietzsche and Schopenhauer, and roamed the countryside in homemade clothes; today we’d call them hippies (with the difference that they idealized war in general and World War I in particular).

But by the late 1920s, Germany’s economic instability and sense of stagnation made such groups seem irrelevant. By contrast, the Nazi Party looked young and efficient, and attracted recruits accordingly: The HJ boasted 100,000 members by early 1933, when Hitler assumed power, 2 million by the end of that year and 5.4 million by the end of 1936. The inevitable “draft” into the Hitler Youth began in March 1939: Everyone age 10 through 18 was forced to join. By then, Hitler understood that the HJ could train young people for immediate entry into the armed forces.

To that end, it was crucial to curb formal education and abstract thinking. By the end of the ’30s, teachers were encouraged to wear HJ uniforms to school, and a new category of “liaison teachers” was formed, answering directly to the HJ. The length of formal education was shortened by one year, and a set of Adolf-Hitler-Schulen (“Hitler Schools”) was established. Today it’s almost comical to think about how these schools divided the academic day: Ninety minutes for book learnin’, five hours for sports. But it’s less amusing to read that boys were chosen for these special schools based on their “character,” a quality deemed superior to intellect and based on Nazi notions of honor, bravery and devotion to the Führer.”

Gee, where else have we heard lately about “character” and blind devotion being valued above intellect? It’s a historically insensitive analogy, to say the least, yet something about it sticks. Maybe it’s just that anytime religious certainty infects politics the result bears a fascist echo.

Speaking of faith-based programs, the Nazis promoted certain young women in the League of German Girls (or BDM, the female branch of the HJ) into something dubbed “Faith and Beauty.” This elite group was made up of gorgeous Aryan types, age 17 to about 28, who were supposed to meet weekly, wear glamorous outfits and look forward to bearing gorgeous Aryan children to S.S. leaders. Since many of those leaders were already married, bigamy was seen as, alas, a eugenic necessity. Throughout, Kater traces the misogyny of Nazi policies: The BDM itself was seen as an apolitical organization, preparing 10-to-18-year-old girls to be good mothers (their main role in Nazi society). Yet it didn’t neglect to teach the girls fierce racist propaganda about perverse Jewish gynecologists and a girl’s duty to remain racially pure (which translated, of course, into an implicit sanction on the “right” kind of sexual activity).

It seems that during the second half of the ’30s, teenagers in the HJ and the BDM were making a lot of whoopee. Kater draws a vivid picture of that generation’s sexual license, brought on, paradoxically, by Nazi racial doctrines. It makes sense that the Third Reich was oversexed; its entire raison d’être was tied to the reproductive rights of various races. Still, some of Kater’s examples will knock you over: Following the now-infamous 1936 Nazi Party rally in Nuremberg, for instance, 900 BDM girls came home pregnant.

By the end of that decade, the Nazis were using “uncontrolled sexuality” as an excuse to send rebellious, non-HJ and non-BDM teens to concentration camps — not for their own good, mind you, but because they endangered the racial purity of the Volk. Kater devotes one long chapter to the German teens who dissented against the Hitler Youth and the BDM. Some of the groups, like the White Rose, bravely distributed fliers deriding Nazi policies, but just as many of these young rebels were anti-Nazi mostly because they were into swing music or petty crime. Anyway, by the end of the war they were all but wiped out — by 1945, a staggering nine out of 10 German youths belonged to the HJ or the BDM. Kater quotes writer Heinrich Böll, who was 16 in 1933, as one of the exceptional few who simply refused to join: “I just could not go to the HJ and I did not go, and that was that.”

If a few individuals had the moral vision to make such blunt choices, what kind of responsibility attaches to the rest? Full responsibility, according to Kater. He finally tackles this problem in the book’s last pages, also outlining the “denazification” procedures adopted by the Allies after the war. (Among other things, the Allies instated a general amnesty on young people’s political crimes.) But at this point in “Hitler Youth,” having read 250 densely packed pages about the country’s two-decades-old, all-pervading faith in Nazi doctrine, you’re hit by the hopelessness of inculcating tolerance and democracy in such a population. And the Allies’ methods for winning over hearts and minds sound absurdly feeble: Teens were “taught democracy” at seminars, invited to sample American culture at nationwide Amerika-Häuser and wooed by the music on U.S. radio stations. Behind such cultural incentives, of course, lay the fact that the country had been devastated and forced to submit unconditionally to Allied forces. Ultimately, Germans had no choice but to change.

Kater, though, remains ambivalent about how deeply democratic ethics took hold among younger people: In the first few years after the war, he writes, “an appreciable number of adolescents were still exhibiting racist patterns of prejudice.” Even after racism seemed to peter out, in the ’50s, young people generally mistrusted any authority or any political conviction. In the aftermath of World War I, W.B. Yeats had written that “the best lack all conviction,” but following 1945 such a renunciation lost its claim to sincerity. When you read the words of a former BDM girl, explaining in 1946 why she can’t believe in democracy — “Are we sure today that perhaps in a few years we will not again be called criminals, because we are now supporting one of the existing political parties?” — you simply want to slap some conscience into her.

Yet it’s possible that she joined the BDM when she was only 10 years old because that’s what all her friends were doing, and because the uniforms were spiffy. Kater repeatedly returns to this maddening difficulty in thinking about the Hitler Youth: At what point did they become guilty? At age 12, or 13, or 15? The urgency of this question underlines how children intensify the moral issues at stake in a totalitarian society. Just watch the legendary Nazi documentary “Triumph of the Will” to see how the feelings prompted by Nazis are amplified in their (indoctrinated) children: The 1934 propaganda film includes panoramas of Nazi rallies and snippets of Hitler’s speeches, but it’s the little Nazi cherubim, marching and drumming and Heiling and blinking, who steal the show. The camera lingers on each small sunlit face, unfolding each child’s individuality even as all the children’s expressions melt into a single gaze of hero worship.

Yet the horrible fascination of these kids can’t be pinned entirely on Leni Riefenstahl‘s skills as a director. Within the greater Nazi nightmare, the Youth are uniquely frightening. The particulars of their frightfulness are well sketched in Kater’s study, though for the ambience of horror you’ll have to turn to a more imaginative book. Given how much horror we have to go around these days, that may be just as well.