The Department of the Missouri was a command echelon of the "United States Army in the 19th century and a sub division of the "Military Division of the Missouri that functioned through the "Indian Wars.
Following the successful conclusion of the "Mexican-American War, the administration of the United States Army was theoretically directed, under the President of the United States, by the "Secretary of War and the "general in chief. In practice the Secretary of War and the heads of the army's staff agencies—who reported directly to him (adjutant general, quartermaster general, commissary general, inspector general, paymaster general, surgeon general, chief engineer, colonel of topographical engineers, and colonel of ordnance)—exercised full authority, leaving the general-in-chief a figurehead. With a lack of central direction, policy and strategy were de facto developed by the commanders of the numbered geographical departments and three division headquarters. After October 31, 1853 the division echelon was eliminated and the six western departments consolidated into four (Departments of "Texas, "New Mexico, "the West, and "the Pacific), whose department commanders employed their troops as they saw fit. The system returned to six departments in 1858 when the Department of Utah was created in January, and the Department of the Pacific split into the Departments of California and Oregon in September.
Military activity affecting one department often originated in another department, preventing efficient use of limited manpower and coordination of efforts. Friction between the Secretaries of War and the generals in chief, and particularly between "Jefferson Davis and "Winfield Scott, obstructed reforms in the staff system that might have brought unity of command and "civilian control of the military. The expansion of the army during the Civil War saw a proliferation in the numbers of geographic departments and their subordinate districts, often changing names and areas under their individual control, some departments eliminated or renamed, only to be recreated again in altered form.
The Department of Missouri resulted from the reorganization and breakup the "Department of the West on November 9, 1861, after "Abraham Lincoln fired "John C. Frémont when he would not rescind his order emancipating the slaves of Missouri and imposing "martial law on the state. "David Hunter served briefly as the last commander Department of the West. The new department included "Missouri, "Arkansas, "Illinois, "Kentucky west of the "Cumberland River and at times, "Kansas. It briefly merged with the Department of Mississippi in 1862, but was recreated September 19, now consisting of Missouri, Arkansas, Kansas, and the "Indian Territory. "Colorado and "Nebraska were added on October 11, 1862, and the department became generally known as the "Department of the Missouri. From 1862 to 1865 the department was primarily concerned with fighting Confederates in Missouri and Arkansas.
The "Department of Kansas was created for a third time on January 1, 1864, removing major areas from the military jurisdiction of the Department of the Missouri. The new commander of the Department of Kansas, Maj. Gen. "Samuel R. Curtis, had two districts (Colorado and Nebraska) wholly involved in Indian warfare, but Curtis was absorbed with fighting Confederates in the Indian Territory and bushwackers in Kansas, allowing his other districts, but particularly Colorado, complete autonomy. Governor "John Evans and Colorado district commander Col. "John M. Chivington took advantage of this lack of oversight to aggressively attack "Cheyenne villages in April 1864, igniting a "major Indian war in July. Curtis created a new District of the Upper Arkansas, to wage the war but he was wholly incapable of locating his opponents. In his other "District of Nebraska, the "warfare was even more intense, but the forces there too weak to deal with it.