For decades, the Vatican had demonized those it saw as the beneficiaries of the much-vilified Enlightenment: liberals, Masons, Jews, and Protestants. It cast all as doing the devil's work, seeking to undermine people's faith in the one true religion. Throughout Italy, the Catholic press stoked this fear. Pius XI largely shared in this world view. In his 1928 encyclical, Mortalium animos, he forbade Catholics to take part in groups that encouraged interfaith dialogue.
David I. Kertzer, The Pope and Mussolini: The Secret History of Pius XI and the Rise of Fascism (2014)