Complex sentence: Due to delays caused by hurricane damage, and then the outbreak of the American Civil War, the fort was never garrisoned, and by the end of the war improvements in artillery had made the fort's design obsolete.
Split into simpler sentences: Due to delays caused by hurricane damage, and then the outbreak of the American Civil War, the fort was never garrisoned. By the end of the Civil War, improvements in artillery had made the fort's design obsolete.