Complex sentence: The occupying Nazis arrested him in 1938 because he was Jewish and an advocate of Austrian independence, Bettelheim imprisoned in the concentration camps of Dachau and Buchenwald for ten and a half months and released in 1939, at which time he emigrated to the United States.
Split into simpler sentences: The occupying Nazis arrested him in 1938 because he was Jewish and an advocate of Austrian independence. Bettelheim was imprisoned in the concentration camps of Dachau and Buchenwald for ten and a half months and released in 1939, at which time he emigrated to the United States.