Complex sentence: Lt. Whiting spent the five years before the Civil War improving rivers, canals, and harbors in North Carolina, South Carolina, Georgia, and Florida, promoted to captain, corps of engineers, in 1858.
Split into simpler sentences: Lt. Whiting spent the five years before the Civil War improving rivers, canals, and harbors in North Carolina, South Carolina, Georgia, and Florida. He was promoted to captain, corps of engineers, in 1858.