The incomprehensibility of the Holocaust is no less true for being a truism. And it extends beyond the obvious historiographical no man's land: How to explain genocidal anti-Semitism in Germany? For everywhere we turn in Essays on Hitler's Europe we find imponderables. Why did Bulgaria refuse to deport Jews from within its own borders, yet give up practically all the Jews who lived in the territories it occupied? Why did Romania, one of only two Nazi satellites that carried out mass exterminations on its own initiative, stop persecuting Jews well before it turned against Germany? Why did Pope Pius XII hide Italian Jews after having done nothing to warn them about their imminent fate? How can we compare the behavior of French and Polish "bystanders," when the punishment for assisting Jews in France varied, and Poles caught doing so were executed, along with their families? In the countries allied with Germany–Romania, Finland, Hungary, Bulgaria and Italy–proportionately, more Jews survived the Second World War than in anti-Nazi Poland and the democratic Netherlands: Why?

These are just some of the questions István Deák raises in his new book. Hitler's Europe consists of review essays that Deák wrote over the past eighteen years, mostly for The New York Review of Books and The New Republic. In its first three parts it addresses, among other topics, Hitler's popularity among everyday Germans, the debates over Daniel Goldhagen's Hitler's Willing Executioners, Victor Klemperer's diaries, German Jews who collaborated with the Nazis and the ambiguities of Italian Fascism. Much of this is familiar ground. By uncovering complexities that other scholars have passed over, Deák does us the great service of making that ground less familiar. For example, when I Will Bear Witness, the diaries Klemperer wrote during the Third Reich, appeared in English several years ago, many critics and scholars hailed them as a triumphant deed and their author as an inspired humanist. A German Jew whose marriage to an "Aryan" kept him out of the camps, Klemperer took it upon himself to "bear precise witness," creating a unique record of life in Nazi Germany. Deák shares the general enthusiasm for the book's richness as a historical source. And he, too, admires Klemperer's courage: Had his journals been found Klemperer probably would have been put to death. However, without any revisionist bravado Deák also directs our attention to Klemperer's misanthropy. This includes the cruelty with which Klemperer treated the people who risked their lives to help him, his gratuitous recklessness with their safety (Klemperer names these resisters in his journals, thereby endangering them), his Schadenfreude toward fellow victims.

But Deák is even more effective in a less well-trodden area. For various reasons, such as the new availability of sources, it might be the most dynamic in Holocaust studies: the Holocaust in Eastern Europe. This is Deák's field. It is also where his roots are, a fact that he laconically adverts to as he discusses certain fateful Eastern European resentments. "As a former Hungarian, I would like to add that the grumblings of the East Central Europeans about a callous, uncaring, and ungrateful West are, in fact, not wholly unwarranted." Deák also tells us that he experienced the "fascist rule" of the Hungarian Arrow Cross, although he does not say just how he experienced it. A longtime professor at Columbia University, Deák has produced a number of influential works on Hungarian history. And while all of the carefully argued, elegantly written essays in Hitler's Europe will inform and impress, Deák is at his most redoubtably erudite when he reviews books that deal with Hungary, Poland, Romania and Lithuania during the Third Reich.

Reviewing historical studies is like translating poetry–at least in one basic respect. The latter activity entails choosing between sound and sense, the former between text and context. For space limitations make it hard to interrogate a work thoroughly while acquainting readers with its topic. And unless the book under review analyzes a well-known, uncontroversial subject, it will be hard to express the significance of its claims without acquainting readers with its topic. Deák's reviews are unrhymed. Of course, he engages with authors and their hypotheses, but the substance of his essays lies in his own narratives of the historical developments at issue. For example, his review of Thomas Sakmyster's book about Miklós Horthy, Hungary's Admiral on Horseback, offers intricate accounts of Horthy's path to power and of the difficulties he faced in answering his country's Jewish Question. We learn that Horthy owed his greatest triumphs to the Nazis, who enabled him to take back land Hungary had lost after World War I, and that Horthy was an anti-Semite who regarded Hitler's plans for the Jews as impractical and inhumane, in that order. We also learn about the Hungarian fascists who pressured him. Horthy set himself up to be squeezed. In the end, that is what happened. The Nazis even kidnapped his son to secure his compliance, for he had not acquiesced in all of Hitler's demands. Horthy argued that the "war industry" would not survive without Hungary's 825,000 Jews whenever Hitler pushed him "to take drastic measures" against them. Could he have done more? Probably not, Deák suggests. He adds that this hardly exculpates Horthy.

Yet Deák does not simply give us a balanced interpretation, according to which the theory "that Hungary collaborated with the Germans mainly to save Jewish lives is unconvincing," as is the widely held "belief…that Hungary could and should have resisted the Germans outright." With his next remark Deák unsettles our equanimity:

Horthy was right in arguing that the Jewish community would have been annihilated had Hungary resisted. Such was the case in Poland and in the Netherlands. It is true that anti-Jewish legislation in Hungary prepared the way for the wholesale robbery of Jewish property as well as for the 1944 deportation by brutal gendarmes of nearly half a million Jews before the eyes of an indifferent public. But it is also true that in such countries as France–where there had been no anti-Jewish laws before the German occupation–thousands of Jews were also deported by brutal French gendarmes before the eyes of an indifferent public. Meanwhile, in fascist Italy–where Mussolini had introduced some anti-Jewish measures as early as 1938–the public (and the Italian occupation forces in France and Yugoslavia) sabotaged the efforts of the Germans and their Italian henchmen to deport Jews to Auschwitz.

If we want to emphasize the causal link between the discriminatory laws that existed in Hungary before the Nazi takeover, and the atrocities that followed it, we should be able to locate analogous connections elsewhere. But when we broaden our scope, a welter of counterexamples confronts us. That France did not have such legislation mattered little. There, similar indifference greeted similar brutality. So how can we be sure that uncoerced anti-Semitic laws in Hungary facilitated what happened later, under Nazi supervision? This is not an isolated problem. In "Poles and Jews," for instance, which first appeared in the New York Review of Books, Deák cites events that militate against recent arguments about the extent of Polish anti-Semitism. Even as he tries to explain the notorious depth of anti-Semitism in Poland, Deák reminds us that "there are more trees at Vad Yashem in Jerusalem dedicated to the memory of Polish helpers of Jews than all such memorial trees combined." Deák shows that although large, terrifying trends dominate the landscape in Hitler's Europe, general tendencies–the kind that bolster historical understanding–are scarce.

"Horthy was right in arguing that the Jewish community would have been annihilated had Hungary resisted": Most historians focus on the causes of actions and their effects. In Holocaust studies, by contrast, inaction is a major theme. The reasons for this range widely, from the sense that Jewish victims displayed passivity, to the ways in which the criminal character of the Holocaust determines scholarly approaches to it. Inaction matters here partly because inaction in the face of crime is a moral problem, one that cries out for historical scrutiny. When Deák asks what might have happened if Horthy had resisted, he does so to illuminate Horthy's constraints, or the roots of his inaction, and also to test the plausibility of Horthy's justification for not acting. What if he had defied Hitler? Just as Horthy himself maintained, the consequences for Hungary's Jews would have been catastrophic. Indeed, Hungary's two attempts to reach an armistice with the Allies resulted in "massive slaughter of the jews." This means that Horthy easily could have believed his own claim. We cannot know for sure. Yet we can say, as Deák does, that opportunism and indifference alone probably do not account for his passive behavior. Deák has evoked Horthy's moral resonance. Accordingly, he writes, Horthy "was not an evil man, but he was not a humanitarian either."

Such "what would have happened if" questions do more than help historians to assess character and assign responsibility. By their nature they argue for a principle that sometimes gets lost in discussions of the Holocaust: Things could have turned out otherwise. These gestures are important. However, set in the wide-open subjunctive mood, they build momentum fast and often go too far. Deák makes this point in the fifth and final part of Hitler's Europe, which reckons with two famous "what if" questions. What if Pope Pius XII had been less conciliatory toward Hitler? And what if the United States and Britain had bombed the gas chambers? His answers are sobering in both cases–especially in the latter:

But let us assume that such raids would have been successful and that only a limited number of inmates of the camps would have been killed even though some of the barracks were only a few hundred yards away from the gas chambers. And let us assume further that many inmates would have managed to escape. Where would they have gone, without any knowledge of the Polish language (by then most Polish Jews were dead), emaciated and dressed in prison garb? In Poland, the penalty for hiding Jews was the execution of the host and his entire family. And even if all the gas chambers and crematoria were destroyed, experience had already demonstrated to the Allies that even greater complexes could become functional again in just a matter of weeks. (In August 1943 the US Army Air Force sacrificed more than 500 airmen and fifty-four bombers in an attempt to smash the vast Romanian oil refineries in Ploesti, which were vital to Germany. Despite horrifying losses, the raids destroyed nearly half of Ploesti's total capacity; within weeks, however, the refineries were producing again at a higher rate than before the raid.) Moreover, the Germans would have been able to fall back on their time-honored method of shooting their victims. And if the rail lines had been bombed? The inmates in the cattle cars and those at the departure points would have been allowed to die of thirst, of the heat or of the cold while the lines were being repaired.

Deák puts the factual complexity of the Holocaust into his contrary-to-fact scenarios. As a result, they offer only bloody alternatives to a bloody reality, and little reason to impugn the United States and Britain for not trying to destroy the Nazi killing machines. Where the book that he is reviewing in this instance, Richard Breitman's What the Nazis Planned, What the British and the Americans Knew, suggests otherwise, it loses sight of the intransigence of its topic. But here as well there are twists: Deák agrees with some of Breitman's main criticisms. Not only did the United States and Britain know more about the Final Solution than they let on; according to Deák they could have done more to help. Late in the war they could have pressured Hitler's allies to undermine his genocidal practices. By then the outcome of the war had become clear, and the prospective victors had leverage. What prompted the inaction? Deák asserts that strategic issues, like the vagueness of their knowledge about the camps and the scarcity of flight crews skilled at precision bombing, deterred the United States and Britain from combating the Final Solution more aggressively. Yet he states that Anglo anti-Semitism probably did too. And so Hitler's Europe concludes by showing how the historiographical challenges of the Holocaust extend beyond Europe. Deák's focus, however, generally remains closer to the scenes of destruction. In fact, he recently wrote a characteristically searching essay on Polish collaboration and Bulgarian resistance. So perhaps Essays on Hitler's Europe will have equally unsettling sequels.