Unholy War by David Kertzer

It took the Catholic church a shockingly long time to forgive the Jews for crucifying Christ, especially since, in Christian thought, the cross was inevitable and preordained. Jesus had to die to be revealed as divine.

Only in 1965 did the Jews' official pardon for deicide come from the Vatican. Having got that out of the way, Catholic-Jewish understanding has been coming on apace ever since, as logically it should – since the two faiths are branches of the same family. Pope John Paul II became the first pontiff to visit Rome's synagogue. In the late 1990s, he opened up the Vatican's secret archive so that an honest assessment could be made of Catholic complicity in the virulent anti-Semitism that gave rise to the Holocaust.

An official church commission reported on the documents in 1998 and tried to make a distinction between the traditional but reprehensible anti-Judaism that dated back to medieval times, and the more modern disease of anti-Semitism. Anti-Judaism had taken the form, in the last 200 years, of a social and political antagonism to Jews, the commission said, and on this count found Catholicism guilty as charged. On the count of anti-Semitism, which it defined as a racist hatred of Jews as promoted by fascists, it deemed the church innocent.

It was not a universally acclaimed verdict. Already John Cornwell in Hitler's Pope has savaged the wartime pontiff, Pius XII, for abandoning Jews to their fate without a murmur of public protest. Now David Kertzer, a Jewish scholar from Brown University, has widened the attack. Unholy War details unambiguously the official Catholic hostility to the Jews from the 19th century until the Holocaust.

For any Catholic, the book makes profoundly uncomfortable and shameful reading. Faced with the remorseless brutality, inhumanity and wickedness of men who purported to be doing God's will, talk of the distinction between anti-Semitism and anti-Judaism seems almost insulting to the memory of those who died.

The story Kertzer tells falls into two main parts. For the period from 1814 until 1870, when the popes still clung on to temporal power in the Papal States, covering a large swathe of central Italy, he provides chapter and verse gleaned from secret archives on the prejudices of church officials. While the rest of Europe was abandoning restrictions on Jews, the popes kept their Jewish subjects locked up in ghettos, banned from the professions, and forced to attend lectures by priests on how misguided were their beliefs.

Worst of all were the efforts to convert Jews. It is a subject Kertzer examined to chilling effect in his 1997 book, The Kidnapping of Edgardo Mortara, about a small boy forcibly baptised and taken from his Jewish home in Bologna by Catholic zealots.

Here that sorry tale is multiplied tenfold. Any Jewish man, often eager only to escape the ghetto, who enquired about conversion would find his wife and children seized. If he changed his mind, or if his wife refused to take the Pope's shilling, they were eventually released, but their children would have been baptised at the moment of seizure. Since Christian children could not be brought up by Jews, they would then be handed over to adoptive parents. So much for the church's belief in the importance of the family.

With the reunification of Italy in 1870, such appalling practices stopped. The church's disdain for Jews was now more a matter of words than deeds. Again Kertzer presents a telling case of virulent anti-Semitism in church publications, from senior clerics, and often from the lips of popes. He then links these words with events in Germany, Austria and Italy. As part of the backdrop and efforts to "justify" the Holocaust, they must undeniably have had an impact.

How great that impact was, however, is hard to judge from Kertzer's book. His focus is narrow, so you never get a sense of how central an issue anti-Semitism was for the popes. For instance, the official journal he quotes most as a pedaller of anti-Semitic poison, Civilta cattolica, had by Kertzer's admission a very small circulation. Its influence is never quantified.

Neither is the emphasis given to almost routine verbal attacks on the Jews by church leaders counterbalanced by any suggestion that it may have been part of a different campaign. Their greatest fear in the period was Communism. If it succeeded, Catholic leaders believed, it would destroy the church. Because, often wrongly, they identified many of the Communist leaders as Jews, anti-Communism and anti-Semitism became as one.

This in no way excuses anything Kertzer describes, but it puts it in context. And the weakness of an otherwise outstanding book is that absence of a wider context. Too often, senior Catholic figures float in and out of the narrative as strongly opposed to the anti-Semitic message sent by their colleagues, but no effort is made to assess which side of this debate represented mainstream Catholic opinion.

Of course, it was a more deferential age, when the Pope's word was more likely to be taken as gospel, but Catholics did not suddenly discover the ability to think for themselves, or to champion leaders outside the Vatican inner circle, in the last quarter of the 20th century. Moreover, when someone previously depicted as an anti-Semite appears to have a significant change of heart, Kertzer is apt to underplay it. Nearing death in 1939, Pope Pius XI wept over the fate of the Jews and commissioned a (never published) encyclical attacking anti-Semitism. Kertzer dismisses the whole episode in a few paragraphs.

As a contribution to the rapprochement between Catholicism and Judaism, Unholy War has an important role to play. Unless the church's anti-Semitic past is evaluated honestly, with no attempts to dodge blame, then historic prejudices will remain. As we have begun to realise since 11 September, resentments and misunderstandings between faiths can have tragic consequences.

Peter Stanford's 'Heaven' is published by HarperCollins; he is a former editor of the 'Catholic Herald'