March 1937: Pope Pius XI issues Mit brennender Sorge encyclical, denouncing aspects of Nazi ideology, protesting regime's violations of Concordat and treatment of Catholics, and abuse of human rights.[27] Regime responds with intensification of Church Struggle.[13] Trumped up "immorality trials" against clergy and anti-church propaganda campaign.[13] Christmas 1937 address, Pope tells cardinals "rarely has there been a persecution so grave"[28] 1 July 1937, Confessing Church banned.[citation needed] Martin Niemöller arrested.[29] Theological universities closed, pastors and theologians arrested.[30]