Union Organisations: Trans-Mississippi, Northwest, and Frontier Theatre

Union Organisations: Trans-Mississippi, Northwest, and Frontier Theatre

Go to Western Territories and Pacific Coast Theatre / Pacific Coast Theatre / Western Theatre / Gulf Coast Theatre / Eastern Theatre / Capital and North-Eastern Theatre / Atlantic Coast Theatre for detailed summaries.

This theatre broadly covers the states of Arkansas, Iowa, Kansas, Missouri, Wisconsin, Minnesota, Nebraska, Indian Territory, and adjacent operational regions.
Most of the region between the Mississippi River and the Rocky Mountains had been under the control of the Department of the West. In July 1861, this was renamed as the Western Department and underwent political and military turmoil while the pro-Southern commander, Brigadier-General William Selby Harney, was supplanted. In the short term, Nathaniel Lyon provided bold leadership, but he was soon transferred to the prominent figurehead John Charles Frémont. By November, it was clear that Frémont was ineffective, if not incompetent, and he was replaced by David Hunter in November 1861. During this time, the Department had absorbed the former Department of New Mexico to the west, giving it a confusing eastward and westward facing responsibility.
More importantly, from its headquarters at St Louis, Missouri, the Western Department also attended to the strategically vital region around the confluence of the Missouri, Mississippi, and Ohio Rivers. Almost immediately, the unwieldy and disparate command was rationalised in response to that urgent strategic priority and Major-General Henry Wager Halleck took control. The newly created Department of the Missouri reflected Halleck’s attention on the great rivers from November 1861 until September 1862. While operations continued west of the Mississippi, requiring the creation of numerous Districts, the more decisive actions occurred east of and along the Mississippi, and along the Tennessee River. Straddling two theatres and laying the foundations for subsequent operations between the Mississippi and the Appalachians, the evolution of the Department of Missouri is continued temporarily in Part 3g, the Western Theatre as part of the gigantic Department of the Mississippi, the equivalent of a Military Division, created under Halleck in March 1862.
Kansas became a District of the Department of the Mississippi from March to May 1862 but soon regained its autonomy as the priorities along the frontier evidently diverged from the more conventional actions along and east of the Mississippi. Hunter led the Department until March 1862, when James Gilpatrick Blunt took over the District and then the revived Department. Blunt commanded until the next major reorganisation in September 1862, when the Department of the Missouri regained its earlier focus west of the Mississippi.
In September 1862, the Department of the Missouri was a reorganised and Department of the Northwest created to manage operations in the Trans-Mississippi, Northwest, and Frontier Theatre. Relevant territories were detached from the discontinued Department (Military Division) of the Mississippi and Department of Kansas was discontinued, enabling a more coherent approach to command in the theatre. The Department of the Northwest – led almost continually by Pope -dealt primarily with actions against Native Americans. The Department of the Missouri primarily prosecuted operations against the Confederates and their supporters west of the Mississippi under Curtis, Schofield, and then Rosecrans.
The Department of the Missouri and Department of the Northwest remained the primary commands in the region until January 1864 when the southward advance through Confederate territory necessitated a further reorganisation. The Department of Kansas was recreated to attend to the frontier regions and a new Department of Arkansas was added to manage operations against Confederate-held territory.
As the Union advance against the Confederacy was pressed increasingly into the Trans-Mississippi region from Louisiana, the Department of the Missouri and the Department of Kansas were transferred to a new Military Division of West Mississippi (Trans-Mississippi Military Division). This achieved coordination of effort against the Confederates west of the Mississippi. The Department of Kansas and Department of the Northwest continued with their operations aligned towards Native American affairs and against unconventional pro-Confederate forces.
By January 1865, the Confederate were incapable of extensive operations west of the Mississippi and Union attention returned to the Gulf Coast and east of the Mississippi. When the Military Division of West Mississippi (Trans-Mississippi Military Division) was disbanded the Department of the Missouri and the Department of the Northwest were transferred to their own Military Division of the Missouri, with the Department of Kansas again being discontinued, and taken over by the Department of the Missouri. The Department of Arkansas was connected more to operations by the Military Divisions that managed the Gulf Coast states from Texas to Alabama and so it only joined the Military Division of the Missouri from March to May 1865.

This is an alphabetical Index of each Organisation by Level and then by name 

Details of each specific organisation can be found in the Introduction to Union Military Organisations – Types -by searching for the Level and then the Name of the Organisation

Military Division of the Missouri

Department of Arkansas
Department of Kansas #1
Department of Kansas #2
Department of Kansas #3
Department of the Missouri
Department of the Northwest
Department of the West
Western Department

District of Eastern Arkansas
District of Northern Arkansas (or Northeastern Arkansas)
District of the Upper Arkansas
District of the Border, Kansas and Missouri
District of the Frontier, Arkansas
District of the Frontier (Kansas)
District of the Frontier
District of Iowa
District of Ironton, Missouri
District of Kansas
District of North Kansas
District of South Kansas
District of Little Rock, Arkansas
District of Minnesota
District of the Mississippi
District of Missouri #1
District of Missouri #2
District of Central Missouri #1
District of Central Missouri #2
District of North Missouri #1
District of North Missouri #2
District of North Missouri #3
District of Northeast Missouri #1
District of Northeast Missouri #2
District of Northwest Missouri
District of Southeast Missouri #1
District of Southeast Missouri #2
District of Southwest Missouri
District of Nebraska Territory
First District of the Northwest
Second District of the Northwest
Third District of the Northwest
Fourth District of the Northwest
District of the Plains (Utah, Colorado, and Nebraska)
District of Rolla, Missouri
District of St Louis Missouri #1
District of St Louis Missouri #2
District of Wisconsin

Army of Arkansas
Army of the Border (Kansas)
Army of the FrontierArmy of Kansas
Army of Western Missouri
Army of Southeastern Missouri
Army of Southwestern Missouri
Army of the Southwest
Army of the West
Western Army

VII Corps Arkansas