Complex sentence: He was the only son of Emmanuel Thomas, Count of Soissons and Princess Maria Theresia of Liechtenstein, he succeeded to his fathers titles, Count of Soissons and Duke of Troppau, when he died in 1729.
Split into simpler sentences: He was the only son of Emmanuel Thomas, Count of Soissons and Princess Maria Theresia of Liechtenstein. He became Count of Soissons and Duke of Troppau when his father died in 1729.