Complex sentence: During World War II, her husband acted to subvert German human-rights abuses of people in territories occupied by Germany and became a founding member of the Kreisau Circle, whose members opposed the government of Adolf Hitler.
Split into simpler sentences: During World War II, her husband acted to subvert German human-rights abuses of people in territories occupied by Germany. He became a founding member of the Kreisau Circle resistance group, opposing the government of Adolf Hitler.