While the Lincoln Administration and most Northerners were preoccupied with trying to capture Richmond in the summer of 1861, it would be the little-known Ulysses S. Grant who delivered the Union's first major victories, over a thousand miles away from Washington. Grant's new commission led to his command of the District of Southeast Missouri, headquartered at Cairo, after he was appointed by "The Pathfinder", John C. Fremont, a national celebrity who had run for President in 1856. Fremont was one of many political generals that Lincoln was saddled with, and his political prominence ensured he was given a prominent command as commander of the Department of the West early in the war before running so afoul of the Lincoln Administration that he was court-martialed.

In January of 1862, Grant persuaded General Henry "Old Brains" Halleck to allow his men to launch a campaign on the Tennessee River. As soon as Halleck acquiesced, Grant moved against Fort Henry, in close coordination with the naval command of Flag Officer Andrew Hull Foote. The combination of infantry and naval bombardment helped force the capitulation of Fort Henry on February 6, 1862, and the surrender of Fort Henry was followed immediately by an attack on Fort Donelson on the Cumberland River, which earned Grant his famous nickname "Unconditional Surrender". Grant's forces enveloped the Confederate garrison at Fort Donelson, which included Confederate generals Simon Buckner, John Floyd, and Gideon Pillow. In one of the most bungled operations of the war, the Confederate generals tried and failed to open an escape route by attacking Grant's forces on February 15. Although the initial assault was successful, General Pillow inexplicably chose to have his men pull back into their trenches, ostensibly so they could take more supplies before their escape. Instead, they simply lost all the ground they had taken, and the garrison was cut off yet again.