Complex sentence: Small in stature, but fit through swimming and working out in a health studio, he was rejected from military service during WWII because of a history of rheumatic fever, but joined the Volunteer Defence Corps, where his experiences inspired some fine cartoons.
Split into simpler sentences: Small in stature, but fit through swimming and working out in a health studio, he was rejected from military service during World War II because of a history of rheumatic fever. But joined the Volunteer Defence Corps, where his experiences inspired some fine cartoons.