Overview
The Department of the Trans-Mississippi had been separated from the Western Department on May 26, 1862. It primarily consisted of the four Confederate states west of the Mississippi: Texas, Louisiana, Arkansas, and Missouri; as well as the two Confederate territories: Indian Territory and Confederate Arizona (roughly corresponding to the present-day states of Oklahoma, New Mexico, and Arizona). The command of the area was given to Major-General T. H. Holmes.
Trans-Mississippi was the operational theater for many quasi-independent forces, including Quantrill's Raiders, and the Missouri Bushwhackers.
Read more about this topic: Army Of The Trans-Mississippi