<P> The Union Army was composed of numerous organizations, which were generally organized geographically . </P> <Dl> <Dt> Military division </Dt> <Dd> A collection of Departments reporting to one commander (e.g., Military Division of the Mississippi, Middle Military Division, Military Division of the James). Military Divisions were similar to the more modern term Theater; and were modeled close to, though not synonymous with, the existing theaters of war . </Dd> <Dt> Department </Dt> <Dd> An organization that covered a defined region, including responsibilities for the Federal installations therein and for the field armies within their borders . Those named for states usually referred to Southern states that had been occupied . It was more common to name departments for rivers (such as Department of the Tennessee, Department of the Cumberland) or regions (Department of the Pacific, Department of New England, Department of the East, Department of the West, Middle Department). </Dd> <Dt> District </Dt> <Dd> A subdivision of a Department (e.g., District of Cairo, District of East Tennessee). There were also Subdistricts for smaller regions . </Dd> <Dt> Army </Dt> <Dd> The fighting force that was usually, but not always, assigned to a District or Department but could operate over wider areas . Some of the most prominent armies were: <Ul> <Li> Army of the Cumberland, the army operating primarily in Tennessee, and later Georgia, commanded by William S. Rosecrans and George Henry Thomas . </Li> <Li> Army of Georgia, operated in the March to the Sea and the Carolinas commanded by Henry W. Slocum . </Li> <Li> Army of the Gulf, the army operating in the region bordering the Gulf of Mexico, commanded by Benjamin Butler, Nathaniel P. Banks, and Edward Canby . </Li> <Li> Army of the James, the army operating on the Virginia Peninsula, 1864--65, commanded by Benjamin Butler and Edward Ord . </Li> <Li> Army of the Mississippi, a briefly existing army operating on the Mississippi River, in two incarnations--under John Pope and William S. Rosecrans in 1862; under John A. McClernand in 1863 . </Li> <Li> Army of the Ohio, the army operating primarily in Kentucky and later Tennessee and Georgia, commanded by Don Carlos Buell, Ambrose E. Burnside, John G. Foster, and John M. Schofield . </Li> <Li> Army of the Potomac, the principal army in the Eastern Theater, commanded by George B. McClellan, Ambrose E. Burnside, Joseph Hooker, and George G. Meade . </Li> <Li> Army of the Shenandoah, the army operating in the Shenandoah Valley, under David Hunter, Philip Sheridan, and Horatio G. Wright . </Li> <Li> Army of the Tennessee, the most famous army in the Western Theater, operating through Kentucky, Tennessee, Mississippi, Georgia, and the Carolinas; commanded by Ulysses S. Grant, William T. Sherman, James B. McPherson, and Oliver O. Howard . </Li> <Li> Army of Virginia, the army assembled under John Pope for the Northern Virginia Campaign . </Li> </Ul> </Dd> </Dl> <Dd> A collection of Departments reporting to one commander (e.g., Military Division of the Mississippi, Middle Military Division, Military Division of the James). Military Divisions were similar to the more modern term Theater; and were modeled close to, though not synonymous with, the existing theaters of war . </Dd> <Dd> An organization that covered a defined region, including responsibilities for the Federal installations therein and for the field armies within their borders . Those named for states usually referred to Southern states that had been occupied . It was more common to name departments for rivers (such as Department of the Tennessee, Department of the Cumberland) or regions (Department of the Pacific, Department of New England, Department of the East, Department of the West, Middle Department). </Dd>

Who are the leaders of the army of the dead