Complex sentence: Confederate General Albert Sidney Johnston set up a defense line around Clarksville expecting a land attack; however, the Union sent troops and gunboats down the Cumberland River, and in 1862, captured Fort Donelson, Fort Henry, and Clarksville.
Split into simpler sentences: Confederate General Albert Sidney Johnston set up a defense line around Clarksville expecting a land attack. The Union sent troops and gunboats down the Cumberland River, and in 1862 captured Fort Donelson, Fort Henry, and Clarksville.