Union Army of the Shenandoah The Army of the Shenandoah was a Union army during the American Civil War . First organized as the " Department of the Shenandoah " in 1861 and then disbanded in early 1862 , it became most effective after its recreation on August 1 , 1864 , under Philip Sheridan . Its Valley Campaigns of 1864 rendered the Valley essentially resourceless , a condition which would speed the end of the Civil War . History . 1861 - 2 . Under the command of Major General Robert Patterson before the three month enlistments of a majority of its troops expired , the Department of Pennsylvania operated as the lone element of Union Army in the Shenandoah Valley of Virginia . After achieving a tactical victory at the Battle of Hoke ' s Run on July 2 and contributing indirectly to the Union disaster at the First Battle of Bull Run on July 21 , its unexpired regiments and commanders were absorbed into a new " Department of the Shenandoah " under the command of Major General Nathaniel P . Banks on July 25 , 1861 . Neither Patterson nor Banks referred to his commands as the " Army of the Shenandoah " in official correspondence , and when the Army of the Potomac adopted a Corps structure on March 18 , 1862 , Banks ' command was redesignated as the " V Corps Provisional . " 1864 . The force was next created by order of Ulysses S . Grant on August 1 , 1864 , in response to a raid by Jubal Early and his Confederate army of 15 , 000 on Washington , D . C . , and especially his defeat of Lew Wallace at the Battle of Monocacy Junction . The new Army of the Shenandoah was composed of the Union VI Corps ( commanded by Horatio G . Wright ) , XIX Corps ( William H . Emory ) , and George Crook ' s Army of West Virginia ( VIII Corps ) . It was placed under Sheridan ' s command with orders to repel Early , deal with Confederate guerillas , and press on into the Shenandoah Valley in Virginia . Early , ever the cunning strategist , kept his force moving so as not to be trapped by Sheridan ' s vastly superior force ; his raid had , if anything , a good deal of success for southern morale . Confederate General Robert E . Lee , coming to the conclusion that Early had done all that was practical , ordered Early to return two of his divisions to Richmond and remain to tie up Sheridan . Learning of this , Sheridan waited until Early weakened himself and then attacked at the Third Battle of Winchester on September 19 and then again at the Battle of Fisher ' s Hill on September 20 – 21 . By the end of these battles , Early ' s force was effectively out of the war , and Sheridan proceeded with his secondary orders to destroy the ability of the Shenandoah Valley to produce foodstuffs for the Confederacy , torching farms and more than 2 , 000 mills . Reinforced again in reaction to the threat of Sheridan ' s 31 , 000 - man army , Early moved against Sheridan once more . After a decisive cavalry victory by Union forces under Brig . Gen . George Armstrong Custer at the Battle of Tom ' s Brook , Early ’ s army launched a surprise attack against Sheridan at the Battle of Cedar Creek on October 19 . Initially successful , the Confederates were repelled by a Union counterattack and the Valley was firmly under Union control . Following their victory , portions of the Army of the Shenandoah were detached to Grant at Petersburg and to William Tecumseh Sherman in Georgia . Sheridan himself joined Grant . Command of the army then passed to Brig . Gen . A . T . A . Torbert until June 27 , 1865 , when the force was disbanded for the final time .