Complex sentence: On January 9--11 of 1863, Union forces conducted an amphibious assault on the fortress backed by ironclad gunboats, and destroyed both the fort and the civilian areas of Arkansas Post.
Split into simpler sentences: On January 9--11 of 1863, Union forces conducted an amphibious assault on the fortress backed by ironclad gunboats. They destroyed both the fort and the civilian areas of Arkansas Post.