Pope Pius XII and Poland includes Church relations from 1939 to 1958. Pius XII became Pope on the eve of the Second World War. The invasion of predominantly Catholic Poland by Nazi Germany in 1939 ignited the conflict and was followed soon after by a Soviet invasion of the Eastern half of Poland, in accordance with an agreement reached between the dictators Joseph Stalin and Adolf Hitler. The Catholic Church in Poland was about to face decades of repression, both at Nazi and Communist hands. The Nazi persecution of the Catholic Church in Poland was followed by a Stalinist repression which was particularly intense through the years 1946–1956. Pope Pius XII's policies consisted in attempts to avoid World War II, extensive diplomatic activity on behalf of Poland and encouragement to the persecuted clergy and faithful.
In Poland, Pius XII made "one of his most controversial decisions" regarding the reorganization of dioceses during World War II.[1]