Fort Donelson was a Confederate fort located in Tennessee, built during the American Civil War. It was strategically positioned along the Cumberland River and served as a key defensive point for the South. The fort was named after Daniel Donelson, a local landowner, and was completed in 1861. In February 1862, Union forces led by Ulysses S. Grant launched a successful attack on the fort, resulting in its surrender. This victory was significant as it opened up the Tennessee and Cumberland Rivers to Union naval and troop movements, marking a turning point in the war in the Western Theater.