Complex sentence: He and his brother John A. Chew participated in all Jackson's campaigns until Jackson's death in May 1863; and, despite his youth, Roger Chew was promoted to the chief of the cavalry's guns under J.E.B. Stuart.
Split into simpler sentences: He and his brother John A. Chew participated in all Jackson's campaigns until Jackson's death in May 1863. Despite his youth, Roger Chew was promoted to the chief of the cavalry's guns under J.E.B. Stuart.