at the Third Battle of Chattanooga, eventually causing Longstreet to abandon his Knoxville Campaign and driving Confederate forces out of Tennessee and opening a route to Atlanta and the heart of the Confederacy. Trans-Mississippi theater Background The Trans-Mississippi theater refers to military operations west of the Mississippi River, encompassing most of Missouri, Arkansas, most of Louisiana, and Indian Territory (now Oklahoma). The Trans-Mississippi District was formed by the Confederate Army to better coordinate Ben McCulloch's command of troops in Arkansas and Louisiana, Sterling Price's Missouri State Guard, as well as the portion of Earl Van Dorn's command that included the Indian Territory and excluded the Army of the West. The Union's command was the Trans-Mississippi Division, or the Military Division of West Mississippi. Battles The first battle of the Trans-Mississippi theater was the Battle of Wilson's Creek (August 1861). The Confederates were driven from Missouri early in the war as a result of the Battle of Pea Ridge. Extensive guerrilla warfare characterized the trans-Mississippi region, as the Confederacy lacked the troops and the logistics to support regular armies that could challenge Union control. Roving Confederate bands such as Quantrill's Raiders terrorized the countryside, striking both military installations and civilian settlements. The "Sons of Liberty" and "Order of the American Knights" attacked pro-Union people, elected officeholders, and unarmed uniformed soldiers. These partisans could not be entirely driven out of the state of Missouri until an entire regular Union infantry division was engaged. By 1864, these violent activities harmed the nationwide anti-war movement organizing against the re-election of Lincoln. Missouri not only stayed in the Union but Lincoln took 70 percent of the vote for re-election. Numerous small-scale military actions south and west of Missouri sought to control Indian Territory and New Mexico Territory for the Union. The Battle of Glorieta Pass was the decisive battle of the New Mexico Campaign. The Union repulsed Confederate incursions into New Mexico in 1862, and the exiled Arizona government withdrew into Texas. In the Indian Territory, civil war broke out within tribes. About 12,000 Indian warriors fought for the Confederacy and smaller numbers for the Union. The most prominent Cherokee was Brigadier General Stand Watie, the last Confederate general to surrender. After the fall of Vicksburg in July 1863, General Kirby Smith in Texas was informed by Jefferson Davis that he could expect no further help from east of the Mississippi River. Although he lacked