History: American Civil War (1861-1865)

The Union's key strategist and tactician in the West was Ulysses S. Grant, who won victories at Forts Henry and Donelson (by which the Union seized control of the Tennessee and Cumberland Rivers); the Battle of Shiloh; and the Battle of Vicksburg, which cemented Union control of the Mississippi River and is considered one of the turning points of the war. Grant marched to the relief of Rosecrans and defeated Bragg at the Third Battle of Chattanooga, driving Confederate forces out of Tennessee and opening a route to Atlanta and the heart of the Confederacy.
Trans-Mississippi theater 1861–1865
Guerrilla activity turned much of Missouri into a battleground. Missouri had, in total, the third-most battles of any state during the war. The other states of the west, though geographically isolated from the battles to the east, saw numerous small-scale military actions. Battles in the region served to secure Missouri, Indian Territory, and New Mexico Territory for the Union. Confederate incursions into New Mexico territory were repulsed in 1862 and a Union campaign to secure Indian Territory succeeded in 1863. Late in the war, the Union's Red River Campaign was a failure. Texas remained in Confederate hands throughout the war, but was cut off from the rest of the Confederacy after the capture of Vicksburg in 1863 gave the Union control of the Mississippi River.