American Civil War: A Union victory at the Battle of Fort Donelson gave General Ulysses S. Grant the nickname "Unconditional Surrender".

The American Civil War was a civil war in the United States between the Union and the Confederacy, which was formed in 1861 by states that had seceded from the Union. The central conflict leading to war was a dispute over whether slavery should be permitted to expand into the western territories, leading to more slave states, or be prohibited from doing so, which many believed would place slavery on a course of ultimate extinction.

During the American Civil War, the United States Army, the land force that fought to preserve the collective Union of the states, was often referred to as the Union army, the federal army, or the northern army. It proved essential to the restoration and preservation of the United States as a working, viable republic.

The Battle of Fort Donelson was fought from February 11–16, 1862, in the Western Theater of the American Civil War. The Union capture of the Confederate fort near the Tennessee–Kentucky border opened the Cumberland River, an important avenue for the invasion of the South. The Union's success also elevated Brig. Gen. Ulysses S. Grant from an obscure and largely unproven leader to the rank of major general, and earned him the nickname of "Unconditional Surrender" Grant.

Ulysses S. Grant was the 18th president of the United States, serving from 1869 to 1877. In 1865, as commanding general, Grant led the Union Army to victory in the American Civil War.