<P> In January 1862, Union General George H. Thomas began to advance on George B. Crittenden's position at Mill Springs . In rainy conditions, Thomas' army moved slowly, and Crittenden advanced to meet them before they could be reinforced by forces from nearby Somerset . The battle commenced on January 19, 1862, and favored Crittenden's forces early on . However, in the confusion caused by the rain and fog, Felix Zollicoffer, commander of Crittenden's First Brigade, rode into the midst of the Union forces . A Confederate officer galloped in, yelling at Zollicoffer to inform him of his mistake . Upon being identified, Zollicoffer was shot out of the saddle and killed, disheartening the Confederates and turning the tide of the battle . Thomas' reinforcements arrived, and Crittenden's forces were forced to retreat across the flooded Cumberland River . Many drowned in the process, and Crittenden was given the blame for the debacle . </P> <P> General Johnston learned of Crittenden's defeat at Mill Springs through an account of the battle printed in a Louisville newspaper . However, he had larger concerns, as Ulysses S. Grant was advancing down the Cumberland and Tennessee Rivers toward Forts Henry and Donelson . Union ironclads routed the Confederate river gunboats on the Mississippi River during the Battle of Lucas Bend on January 11, forcing them back to Columbus . Following Grant's victory at the Battle of Belmont, General Polk had anticipated that Union forces would target the Mississippi River and attack Columbus, and had withdrawn most of his forces to that location . Lloyd Tilghman was left to defend Fort Henry with fewer than 3,000 men . Union troops began their assault on the fort on February 5, 1862, and Tilghman surrendered the following day . </P> <P> General Johnston countered by ordering Pillow, Buckner, and John B. Floyd to the defense of Fort Donelson . None of the three was specifically given command, a decision that would prove costly . Grant arrived at Donelson on February 13, and found himself outnumbered by some 3,000 troops . Floyd failed to capitalize on his advantage, however, and Grant was reinforced the next day . On February 15, the Confederates had nearly cleared an escape route to Nashville, but arguments among the generals delayed the retreat . Floyd seized a steamboat and used it to evacuate his forces, while Pillow fled in a rowboat . Buckner, left alone in command, proposed a cease - fire to Grant while terms of surrender were negotiated . Grant's reply--that only "an unconditional and immediate surrender" could be accepted--made him a hero in Union eyes, and earned him the nickname "Unconditional Surrender" Grant . </P> <P> The collapse of Forts Henry and Donelson made Polk's position at Columbus untenable; the Confederates were forced to abandon "The Gibraltar of the West ." His line shattered, Johnston abandoned Bowling Green on February 11, 1862, retreating first to Nashville, then further south to join P.G.T. Beauregard and Braxton Bragg at Corinth, Mississippi . Cumberland Gap, the final piece of Johnston's line, finally fell to Union forces in June 1862 . </P>

What was not an advantage of the north in the civil war