The campaign classification established by the United StatesNational Park Service is more fine-grained than the one used in this article. Some minor NPS campaigns have been omitted and some have been combined into larger categories. Only a few of the 75 battles the NPS classifies for this theater are described. Boxed text in the right margin show the NPS campaigns associated with each section.
The Battle of Glorieta Pass was a small skirmish in terms of both numbers involved and losses (140 Union, 190 Confederate). Yet the issues were large, and the battle was decisive in resolving them. The Confederates might well have taken Fort Union and Denver had they not been stopped at Glorieta. As one Texan put it, "If it had not been for those devils from Pike's Peak, this country would have been ours."
This small battle dissolved any possibility of the Confederacy taking New Mexico and the far west territories. In April, Union volunteers from California pushed the remaining Confederates out of present-day Arizona at the Battle of Picacho Pass. In the Eastern United States, the fighting dragged on for three more years, but in the Southwest the war was over.
Several battles occurred between Confederate soldiers and or militia within Confederate Arizona, the height of the Apache campaigns against rebel forces was during mid to late 1861.
A guerrilla conflict began to wrack Missouri. Gangs of Confederate insurgents, commonly known as "bushwhackers", ambushed and battled Union troops and Unionist state militia forces. Much of the fighting was between Missourians of different persuasions; both sides carried out large-scale atrocities against civilians, ranging from forced resettlement to murder. Historians estimate that the population of the state fell by one-third during the war; most survived but fled or were driven out by one side or the other. Many of the most brutal bushwhacker leaders, such as William C. Quantrill and William T. "Bloody Bill" Anderson, won national notoriety. A group of their followers remained under arms and carried out robberies and murders for sixteen years after the war, under the leadership of Jesse James, his brother Frank James, and Cole Younger and his brothers.
The Union mounted several attempts to capture the trans-Mississippi regions of Texas and Louisiana from 1862 until the war's end. With ports to the east under blockade or captured, Texas in particular became a blockade-running haven. Referred to as the "back door" of the Confederacy, Texas and western Louisiana continued to provide cotton crops that were transferred overland to the Mexican border town of Matamoros, Tamaulipas, and shipped to Europe in exchange for supplies.
Determined to close this trade, the Union mounted several invasion attempts of Texas, each of them unsuccessful. Confederate victories at Galveston, Texas, and the Battle of Sabine Pass repulsed invasion forces. The Union's disastrous Red River Campaign in western Louisiana, including a defeat at the Battle of Mansfield, effectively ended the Union's final invasion attempt of the region until the fall of the Confederacy. Jeffery Prushankin argues that Kirby Smith's "pride, poor judgment, and lack of military skill" prevented General Richard Taylor from potentially winning a victory that could have greatly affected the military and political situation east of the Mississippi River.
Isolated from events in the east, the Civil War continued at a low level in the Trans-Mississippi theater for several months after Lee's surrender in April 1865. The last battle of the war occurred at Palmito Ranch in southern Texas – a Confederate victory.