After the Nazi takeover of power in 1933, the Gleichschaltung transformed the university into a Nazi educational institution. According to the Führerprinzip the autonomous and self-governening administration of the university was replaced by a hierarchy of leaders resembling the military, with the university president being subordinate to the ministry of education. Jewish professors and students and political opponents were ostracized and expelled from the university. The theologian Karl Barth was forced to resign and to emigrate to Switzerland for refusing to swear an oath to Hitler. The Jewish mathematician Felix Hausdorff was expelled from the university in 1935 and committed suicide after learning about his impending deportation to a concentration camp in 1942. The philosophers Paul Ludwig Landsberg and Johannes Maria Verweyen were deported and died in concentration camps. In 1937 Thomas Mann was deprived of his honorary doctorate. His honorary degree was restored in 1946.