Complex sentence: With little thought, the army commanders decide that Jewish Captain Alfred Dreyfus (Joseph Schildkraut) is the traitor, is courtmartialed and imprisoned on Devil's Island in then French Guyana.
Split into simpler sentences: With little thought, the army commanders decide that Jewish Captain Alfred Dreyfus (Joseph Schildkraut) is the traitor. He is courtmartialed and imprisoned on Devil's Island in French Guyana.