The First World War, the Second World War, and the Cold War are episodes of a wider conflict, called here “The Seventy-Five Years War,” dominated the twentieth century. Both unresolved issues and new issues from the First World War carry over into the next conflict, which in turn led immediately to the Cold War. While this great conflict can be viewed from different perspectives, this book focuses on the role of the Papacy. From the stateless Benedict XV’s attempts to call a peace conference, to the establishment of Vatican City and the restoration of sovereignty, to the struggles of Pius XI and Pius XII with both Fascism and Communism, and the contributions of John Paul II to the collapse of Communism, the Catholic Church was a part of this struggle. In addition to its humanitarian and pacifistic efforts from 1914 to 1989, the Catholic Church was also engaged in an intense ideological struggle with atheistic communism. This conflict will often take priority over other ideological conflicts, such as that with Fascism, as well as complicate the Church’s mission in other parts of the world, such as Latin America and Asia.