Complex sentence: In his Absence, Starbuck returns, having spotted the real northern attack heading toward the Confederate left wing and, after some difficulty, convinces Colonel Nathan Evans, senior officer on the confederate left, that an attack is imminent.
Split into simpler sentences: In his absence, Starbuck returns, having spotted the real Northern attack heading toward the Confederate left wing. After some difficulty, he convinces Colonel Nathan Evans, senior officer on the Confederate left, that an attack is imminent.