"By God, nobody was whipped at Pea Ridge but Van Dorn!"
Brigadier General James S. Rains
After the battle, Van Dorn took his army to Van Buren, Arkansas, then to Corinth, Mississippi, where he hoped to join General Albert Sydney Johnston’s Army of Tennessee. His army would be absorbed into the Army of Tennessee after Shiloh, seeing its final major battle at Bentonville, NC in 1865. Van Dorn's Army of the West would never again fight west of the Mississippi River.
After a brief period to rest, reinforce, and resupply his battered command, Curtis resumed the offensive. He received reports that Van Dorn was moving his army to the east. Suspecting that he was going to try to invade Missouri from the southeast, Curtis moved to block Van Dorn. When he learned that the Army of the West had crossed the Mississippi River, Curtis turned his attention southward towards Little Rock, Arkansas's capital.
As the Federals marched south, General Halleck ordered Curtis to send nearly half of his army east to join William Rosecrans's Army of the Tennessee. The loss of so many soldiers and a critical supply shortage forced Curtis to abandon his designs for capturing Little Rock. Instead, he headed south, towards Helena, on the Mississippi River. Curtis cut loose from his supply line and lived off of the land, foraging heavily and destroying everything of an economic or military value that they could not take with them. On July 12, 1862, the Army of the Southwest arrived at Helena. The winter campaign that started in Lebanon, Missouri on February 12 was over.
The Army of the Southwest had marched over 250 miles prior to the battle of Pea Ridge. After the battle, the Federals had marched an additional 500. For the last two weeks of the campaign, they had operated independent of a base of supplies, 11 months before General Grant attempted the same maneuver at Vicksburg and 2 years prior to William Sherman's "March to the Sea" in Georgia. During the campaign through Arkansas's agricultural heartland, the Federals freed a huge number of slaves, issuing them "freedom papers", although Curtis had no authority from the U.S. government to do so. By the end of the campaign, over five thousand former slaves followed the army, while several thousand more fled north into Missouri.
The fighting would continue in Arkansas though. Throughout the summer and fall of 1862, General Thomas C. Hindman pieced together an army to drive the Federals from Arkansas. In December 1862, Hindman was defeated by Generals James Blunt & Francis Herron at Prairie Grove, Arkansas. On July 4, 1863, the Federal Army won an important victory at Helena, Arkansas, when the Confederates would attempt to drive the Federals from the city. In 1864, Sterling Price launched an invasion of Missouri, but was defeated again by his old foe from Pea Ridge, Samuel Curtis.
After Pea Ridge, most of the fighting turned into guerrilla warfare. "Bushwhackers" (pro-Southern Missourians) & "Jayhawkers" (pro-Union Missourians and Kansans) made hit & run raids, ambushed wagon trains, and terrorized the populace. Many of these raiders, though, were more interested in murder, plunder, and settling personal scores than with any military objectives. The most famous attack took place at Lawrence, Kansas in 1863, when 180 citizens were killed and the town was burned and looted by raiders under Captain William C. Quantrill. Some of the most famous outlaws of the "Wild West" period, most notably Frank & Jesse James, and their cousins, the Youngers, rode with these guerrilla bands.