Trans-Mississippi Theater

• Brigadier General John S. MarmadukeElkin's Ferry, Boonville, Independence, Cane Hill, Chalk Bluff, Pine Bluff +8 more
• Major General Sterling PriceWilson's Creek, Lexington, Marmiton River, Prairie D'Ane, Dry Wood Creek, Fort Davidson +4 more
• Colonel Douglas H. CooperNewtonia, Chusto-Talasah, Old Fort Wayne, Round Mountain, Honey Springs
• Major General Richard TaylorPleasant Hill, Mansura, Mansfield, Yellow Bayou
• Brigadier General James F. FaganIndependence, Mine Creek, Marais des Cygnes
• Lieutenant Colonel William C. QuantrillLawrence, Baxter Springs
• Colonel G.W. ThompsonIndependence, Lone Jack
• Major General Thomas C. HindmanHill's Plantation, Prairie Grove
• Colonel Colton GreeneOld River Lake, Clark's Mill
• Brigadier General Tom GreenBlair's Landing, Valverde
• Brigadier General Joseph ShelbyGlasgow, Byram's Ford
• Governor Clairborne JacksonCarthage
• Brigadier General Ben McCullochWilson's Creek
• Colonel James FrazierSpringfield
• Colonel Caleb DorseyMount Zion Church
• Colonel J.T. HughesIndependence
• Colonel Stand WatieCabin Creek
• Colonel Joseph J. CookGalveston
• Colonel X.B. DebrayGalveston
• Major General Earl Van DornPea Ridge
• Captain Joseph FrySaint Charles
• Colonel William H. ParsonsHill's Plantation
• Brigadier General W.L. CabellDevil's Backbone
• Brigadier General James B. FaganMarks' Mills
• Brigadier General Samuel Bell MaxeyPoison Spring
• General E. Kirby SmithJenkins' Ferry
• Lieutenant Colonel William ByrdFort DeRussy
• Brigadier General Hamilton P. BeeMonett's Ferry
• General D. R. AtchisonLiberty
• Brigadier General James S. RainsDry Wood Creek
• Brigadier General M. Jeff ThompsonFredericktown
• Colonel J.A. PoindexterRoan's Tan Yard
• Colonel Joseph C. PorterKirksville
• Colonel Jeremiah Vard CockrellLone Jack
• Colonel Upton HaysLone Jack
• Colonel John Q. BurbridgeClark's Mill
• Brigadier General John B. ClarkGlasgow
• Major Charles L. PyronGlorieta Pass
• Lieutenant Colonel William R. ScurryGlorieta Pass
• Brigadier General Henry Hastings SibleyValverde
• Colonel James McQueen McIntoshChustenahlah
• Lieutenant Colonel John JumperMiddle Boggy Depot
• Major J.S. IrvineSabine Pass
• Major General John B. MagruderGalveston
• Colonel John S. "Rip" FordPalmito Ranch
• Lieutenant Richard W. DowlingSabine Pass II

• Major General Frederick SteeleElkin's Ferry, Prairie D'Ane, Jenkins' Ferry
• Major General Nathaniel P. BanksPleasant Hill, Mansura, Mansfield, Monett's Ferry
• Little CrowFort Ridgely, Wood Lake
• First Lieutenant Timothy J. SheehanFort Ridgely
• Brigadier General Nathaniel LyonBoonville, Wilson's Creek
• Colonel Franz SigelCarthage
• Major General Samuel D. SturgisWilson's Creek
• Colonel James A. MulliganLexington
• Major James ZagonyiSpringfield
• Brigadier General Benjamin M. PrentissMount Zion Church
• Lieutenant Colonel James T. BuelIndependence
• Brigadier General Friedrich SalomonNewtonia
• Major General Alfred PleasontonIndependence, Mine Creek, Marais des Cygnes, Byram's Ford
• Brigadier General John McNeilMarmiton River, Kirksville, Cape Girardeau
• InkpadutaBig Mound, Dead Buffalo Lake, Whitestone Hill, Killdeer Mountain, Stony Lake
• Brigadier General Henry Hastings SibleyBig Mound, Dead Buffalo Lake, Wood Lake, Stony Lake
• Brigadier General Alfred SullyWhitestone Hill, Killdeer Mountain
• OpothleyaholaChusto-Talasah, Round Mountain, Chustenahlah
• Brigadier General James G. BluntOld Fort Wayne, Cane Hill, Prairie Grove, Baxter Springs, Lexington, Byram's Ford +2 more
• Colonel James M. WilliamsCabin Creek, Poison Spring
• Commander W.B. RenshawGalveston, Galveston
• Brigadier General Samuel R. CurtisPea Ridge, Little Blue River, Westport
• Colonel Graham N. FitchSaint Charles
• Commander Augustus H. KiltySaint Charles
• Colonel Charles HoveyHill's Plantation
• Brigadier General William P. BentonHill's Plantation
• Brigadier General Francis J. HerronPrairie Grove
• Brigadier General William VandeverChalk Bluff
• Colonel William F. CloudDevil's Backbone
• Colonel Powell ClaytonPine Bluff
• Brigadier General John W. DavidsonBayou Forche
• Lieutenant Colonel Francis DrakeMarks' Mills
• Black KettleSand Creek
• Colonel John ChivingtonSand Creek, Glorieta Pass
• Brigadier General Joseph A. MowerOld River Lake, Fort DeRussy, Yellow Bayou
• Lieutenant James B. PondBaxter Springs
• Brigadier General A.J. SmithFort DeRussy
• Brigadier General Thomas Kilby SmithBlair's Landing
• Rear Admiral David D. PorterBlair's Landing
• Lieutenant Colonel John ScottLiberty
• Colonel J.H. LaneDry Wood Creek
• Colonel J.B. PlummerFredericktown
• Colonel William P. CarlinFredericktown
• Major W.M.G. TorrenceRoan's Tan Yard
• Major Emory S. FosterLone Jack
• Captain Hiram E. BarstowClark's Mill
• Colonel Samuel MerrillHartville
• Brigadier General Egbert B. BrownSpringfield
• Colonel Chester HardingGlasgow
• Brigadier General Thomas Ewing Jr.Fort Davidson
• Colonel John P. SloughGlorieta Pass
• Colonel E. R. S. CanbyValverde
• Major Charles WilletteMiddle Boggy Depot
• Acting Master Frederick CrockerSabine Pass, Sabine Pass II
• Colonel Isaac S. BurrellGalveston
• Colonel Theodore H. BarrettPalmito Ranch
• Major General William B. FranklinSabine Pass II

West of the Mississippi River lay a distinct arena of Civil War combat known as the trans-Mississippi theater. Generally, historians exclude the Pacific-bordering states and territories from this designation, since those areas made up their own separate theater, the Pacific coast theater, spanning 1861 to 1865.

This article uses a broader classification scheme than the one the National Park Service, part of the U.S. Department of the Interior, applies to the region. The NPS system breaks things down with greater precision, and here some of its smaller campaigns have been left out while others are folded into wider groupings. Of the 75 major battles the NPS attributes to this theater, only a handful receive coverage below. Readers will find the relevant NPS campaign designations noted in boxed text along the right margin of each section.

For much of 1861, fighting in this theater centered on the contested loyalty of Missouri, a border state. Confederate-aligned forces known as the Missouri State Guard claimed significant triumphs at Wilson's Creek and at the First Battle of Lexington, though they suffered a setback and were pushed back during the First Battle of Springfield. By March 1862, a Union army led by Samuel Ryan Curtis had crushed Confederate resistance at the Battle of Pea Ridge in the northwestern corner of Arkansas, cementing federal authority over the bulk of Missouri territory. Guerrilla warfare plagued Missouri, Kansas, and the Indian Territory (what is now Oklahoma) for the remainder of the conflict, with the notorious Lawrence massacre standing out as the most infamous episode, when Confederate raiders struck the pro-Union town of Lawrence, Kansas, in August 1863.

Confederate troops under Henry H. Sibley advanced northward from El Paso, Texas, following the Rio Grande into New Mexico Territory during the spring of 1862. Their early triumph came at the Battle of Valverde, yet their momentum halted at the Battle of Glorieta Pass, fought March 26 through 28 of that year. The following year, General Edmund Kirby Smith assumed leadership of the Confederate Trans-Mississippi Department and attempted, without success, to break the siege Maj. Gen. Ulysses S. Grant had laid against Vicksburg on the Mississippi's eastern shore. That drawn-out campaign culminated in Gen. John C. Pemberton's surrender in July 1863, handing the Union dominion over the whole of the Mississippi River and cleaving the Confederacy into two. Consequently, the Trans-Mississippi Department found itself nearly severed from Confederate territory to the east, earning it the derisive nickname "Kirby Smithdom" for how loosely the Confederate government actually governed it.

During the Red River Campaign of 1864, Major General Nathaniel P. Banks led Union forces in a bid to seize northwestern Louisiana, only to be repelled by Confederate troops under Richard Taylor. That same year, Major General Sterling Price launched what became known as Price's Raid, a bid to wrest Missouri back for the Confederacy, but the effort collapsed when his forces were routed at the Battle of Westport in October. With the Confederacy's other principal armies to the east already having laid down their arms, Kirby Smith formally surrendered his command at Galveston, Texas, on June 2, 1865. Weeks later, on June 23, Stand Watie, commander of Confederate forces in the Indian Territory, became the final Confederate general to lay down arms.

Confederate Territory of Arizona and Federal New Mexico Territory

A push by Confederate soldiers into the newly formed New Mexico Territory, organized in 1851 and covering what would become Arizona and New Mexico, achieved considerable success during 1861. Inhabitants of the southern reaches of the territory passed their own ordinance calling for secession and appealed to Confederate troops based nearby in Texas for help driving out the Union soldiers who remained there. After winning the First Battle of Mesilla on July 25, 1861, near Mesilla, New Mexico, and taking several Union garrisons prisoner, Col. John Baylor declared the existence of a Confederate Territory of Arizona. Pushing north along the Rio Grande Valley, southern troops seized both Albuquerque and Santa Fe by March of 1862. Further gains toward the north stalled, however, and once Union reinforcements arrived from California, the Confederates pulled out of Arizona entirely that same year.

Fought from March 26 through 28, 1862, the Battle of Glorieta Pass involved relatively modest troop numbers and casualties, with 140 lost on the Union side and 190 among the Confederates. Despite its small scale, the engagement carried enormous weight for the strategic and political questions at stake, and its outcome settled them decisively. Had the rebels not been halted here, they stood a real chance of seizing Fort Union farther up the Rio Grande, and perhaps even Denver, seat of the Colorado Territory to the north. A Texan soldier later remarked that were it not for those devils from Pike's Peak, the region would have belonged to them.

With this modest clash, any hope the Confederacy held of claiming New Mexico and the distant western territories collapsed. By April, volunteer troops from California known as the California Column drove the last Confederate holdouts from what is now Arizona in the Battle of Picacho Pass. While combat would continue for another three years back east, the contest against the Confederacy in the Southwest had reached its conclusion. Conflict persisted, though, against the Apache, Navaho, and Comanche, and California's garrison troops carried on that fight until regular U.S. Army units took over following the war's end.

Confederate troops and militia clashed repeatedly within the borders of Confederate Arizona, and Apache resistance against the rebel presence peaked during the middle and later months of 1861.

Missouri, Arkansas, and Kansas

Missouri entered the war as a slave state with a fierce and organized secessionist faction, yet its people ultimately backed the Union by roughly two or three to one, a legacy partly rooted in the pro-slavery "border ruffians" who had clashed with antislavery militias in Kansas during the 1850s. Claiborne F. Jackson, the state's pro-Confederate governor, joined his modest state guard, commanded by General Sterling Price, with Confederate troops led by General Ben McCulloch. This combined force won engagements at Wilson's Creek and at Lexington, Missouri, but the tide turned when substantial Union reinforcements arrived in February 1862 and pushed the rebels out of the state altogether. Their hopes of returning were extinguished at Pea Ridge, Arkansas, where they suffered defeat between March 6 and 8.

What followed was years of irregular warfare that tore at Missouri's communities. Bands of Confederate raiders, known as bushwhackers, staged ambushes and skirmishes against Union soldiers and pro-Union state militia units. Because so much of this violence pitted Missourians against fellow Missourians, both factions committed sweeping abuses against civilians, from forced expulsions to outright killing. Scholars believe the state's population shrank by roughly a third over the course of the conflict, as most residents who vanished had either fled or been forced out rather than perished outright. Some of the era's most infamous guerrilla commanders, including William C. Quantrill and William T. "Bloody Bill" Anderson, achieved lasting notoriety across the country. Long after the fighting ended, a faction of their former fighters kept up an armed campaign of theft and killing, activity some viewed as continued guerrilla resistance, for sixteen years, under men such as Jesse James, his brother Frank, and Cole Younger together with his own brothers.

By nearly every measure, Missouri's Confederate guerrilla struggle stands as the most severe conflict of its kind ever waged on American ground, with estimates placing the death toll near twenty seven thousand. Scholars have proposed several reasons for this unusually intense violence, one being its possible connection to the thousands of forced property sales imposed by courts on Confederate sympathizers, a pract