There is currently a controversy, or renewal of a controversy, about the role of Pope Pius XII and the Jews in during World War II. It is usually posed by mainstream accounts as: did Pius XII do all he could to save the Jews from the Holocaust? Since the current Pope, Benedict XVI, was a member of the Nazi youth organization and is trying to get Pius XII qualified as a saint, now is a good time to get the facts about Pius XII.
"Politics makes strange bedfellows." Here I find myself siding with the State of Israel, whereas I am usually pro-Palestinian (the Palestinians have nothing to do with this particular controversy). Israel, and doubtless many Jewish organizations, don't want Pius XII canonized.
Pius XII, before he became Pope, was the Vatican Secretary of State. Born Eugenio Pacelli, as Cardinal Pacelli he was the right-hand man to Pius XI. To understand Pius XII you have to understand Pius XI, who chose to promote Pacelli to the second highest rank in the Roman Catholic Church.
I think it is fair to say that Pius XI, who became pope in 1922, was the architect of fascism. Of course this is a controversial hypothesis, and can be argued against on a number of fronts. Benito Mussolini would be the other candidate for the title. But it was Pius XI who made anti-Communism the first priority of the Catholic Church. Under the banner of Anti-Communism (and the Church was also openly against democratic forms of socialism, and even capitalist forms of democratic government), Pius helped first Mussolini, then other fascist leaders come to power. I know that is a shocking assertion to most people, but it is not difficult to paint that picture once the facts are at hand. First, however, I want to relate this to antisemitism and thus the Holocaust.
Adolf Hitler is usually portrayed as the architect of the Holocaust. His own antisemitism, in the consensus histories, is attributed to anti-semitic cults that he encountered as a young man living in Vienna. However, this does not hold up under analysis.
Hitler was born a Catholic (See Hitler's Catholicism) and was raised as a Catholic in a Catholic state, the Austro-Hungarian Empire. Antisemitism in Austria was rooted in the Catholic Church. There was a close alliance between the Hapsburg emperors and the Church, which ran the education system under the tender mercies of the Jesuits. When modern ideas began to penetrate the empire in the 19th century and some representative government was allowed, an Austrian Catholic Party (Later the Christian Social Party) was formed, with the Church's blessing. Because the Church itself was be abandoned by so many citizens in the empire, the party's leader, Karl Lueger, hit upon antisemitism as the primary selling point.
The antisemitism of the Holocaust grew out of the antisemitism promoted by the Catholic Church throughout its history. It became enshrined as a principle of fascist government because the Church wanted its prejudices to be backed by the power of the state.
To consider the idea that Pius XI was the architect of modern fascism, see the following essays (they are in linear order):
Pius XI and the Rise of Benito Mussolini
Pius XI and the Rise of Adolph Hitler
Pius XI and the Rise of General Franco
Pius XI, the Rise of Petain, and Fascist Vichy France
Pius XI and his Secretary of State were deeply involved in promoting fascism in other nations, notably Poland, Czechoslovakia, and Austria as well.
So when Cardinal Pacelli became Pope on March 2, 1939, he had been part of setting up a series of fascist regimes in Europe. Fascist movements, mostly but not exclusively Catholic, existed in many more nations of the world, including in the United States. He was a gung-ho anti-communist who believed that fascist dictators were the best bulwark against atheist communism, and against all rival creeds. Better still, except for Hitler, who had a large Protestant Christian population to deal with, all the dictators made the Catholic Church their exclusive religious partner. Cardinal Pacelli had never spoken out against anti-Semitism. He did not even speak out against mass-murder of non-Catholics, which had just been carried out by the Spanish fascists under General Francisco Franco. Here's what he said:
"With great joy we address you, dearest sons of Catholic Spain, to express our paternal congratulations for the gift of peace and victory, with which God has chosen to crown the Christian heroism of your faith and charity ... As a pledge of the bountiful grace which you will receive from the Immaculate Virgin and the Apostle James, patrons of Spain ... we give to you, our dear sons of Catholic Spain, to the Head of State and his illustrious Government, to the zealous Episcopate and its self-denying clergy, to the heroic combatants and to all the faithful, our apostolic benediction."
That said, I don't think that Pius XII agreed with the technical details of Hitler's extermination of the Jews. Hitler saw the Jews as not just a religion, but as a race of people. Pius XII and the Catholic Church had a long history of giving Jews (and other non-Catholics) the choice of conversion or death. I believe that if Pius XII had run Hitler's concentration camps for Jews he would have gone to great lengths to convert them to Catholicism. Hitler did not give the Jews that opportunity.
You might say that Pius XII does not sound like much of a saint, but you are using your own definition of a Saint, not that of the Roman Catholic Church. There are many Saints who were mass murderers. As long as they killed non-Catholics, with the idea in mind of converting the survivors to Catholicism, they are considered to be heroes of the church.