An active opponent of Nazism, he signed (1934) the Barmen Declaration in protest against attempts by German Christians to synthesize Nazism with Christianity. He was forbidden by the government to teach, and in 1937 his seminary at Finkenwalde was closed. In 1942 he tried to form a link between the Germans opposed to Hitler and the British government. Arrested in 1943, he was sent to Buchenwald concentration camp, where he was hanged in 1945.