Complex sentence: He was in Spain in 1937 during the Spanish Civil War, when the murder of his friend José Robles soured his attitude toward communism, and led to severing his relationship with fellow writer Ernest Hemingway.
Split into simpler sentences: He was in Spain in 1937 during the Spanish Civil War. The murder of his friend José Robles soured his attitude toward communism, and led to severing his relationship with fellow writer Ernest Hemingway.