Complex sentence: Tom O'Flaherty was an Irish-American Communist politician in the early 20th century; supporter of the Trotskyist James P. Cannon, and brother of the famous Irish writer Liam O'Flaherty.
Split into simpler sentences: Tom O'Flaherty was an Irish-American Communist politician in the early 20th century. Brother of the famous Irish writer Liam O'Flaherty.