Missouri was vital to the Union cause. If it went to the Confederacy and became an active Confederate area, Union forces would not have been able to move down the Mississippi. In order to hold Missouri for the Union, Kansas had to be protected. Once Missouri was more or less secure, the Union had to press large Southern forces out of Arkansas. The Union managed to do all of these things, but it took a great deal of time and effort, and Kansas, Missouri, and Arkansas were never entirely free of Southern influence and forces.

Kansas

Kansas was the scene of fighting even before the Civil War broke out in 1861. Having been a territory that would be admitted to the Union based on popular sovereignty, that is, how many of its enfranchised population voted to have the state admitted as a slave or free state, both Northerners and Southerners raced to the region in the 1850s to bolster support for their respective views. Fighting broke out between groups of the opposing ideologies, and the territory became known as “Bleeding Kansas.” Roving fighters were not averse to mayhem and murder.

The most notorious partisan raid was carried out by a band led by William Quantrill against the town of Lawrence. Quantrill led his guerillas into Lawrence to avenge the deaths of Missourians imprisoned by Federal authorities; a jail roof had collapsed, killing a number of women. Before Quantrill's men left, much of the town was destroyed and more than 150 men and boys lay dead.

A month and a half later, Quantrill's Raiders fought elements of a Union force near Baxter Springs near the southeast corner of the state. The partisan group of 400 defeated the Union men, then rode on south to spend the winter in Texas.

The only battle in Kansas between regular Confederate and Union forces took place at Mine Creek in October 1864. This was during the Sterling Price raid up through Missouri and continued while Price was attempting to return to Arkansas. Union cavalry under Alfred Pleasonton defeated Price, who continued his retreat southward.

Missouri

Missouri suffered the same sort of partisan warfare as Kansas, though it did not see as much violence before the war began. Missouri was a slave state, but there was considerable sentiment to stay in the Union. The governor at the time Fort Sumter was attacked was pro-Confederacy, but the legislature was not inclined to secede. A stalemate ensued between pro-Northern and pro-Southern troops in and around St. Louis.

Washington sent a feisty soldier named Nathaniel S. Lyon to command the Union troops. In May, Lyon broke up the pro-Southern militia but then got into a fight marching back into St. Louis; twenty-eight civilians were killed, but Missouri stayed in the Union despite its status as a slave state.

Lyon then marched his men into southwest Missouri, the stronghold of Southern sentiment. At Wilson's Creek on August 10, 1861, Lyon fought a Confederate force under Sterling Price and Benjamin McCulloch. Lyon was killed in the hard-fought battle and the Federals were repulsed. But the Rebels could not make much of their victory, and the state was not threatened with a Southern advance. General John Fremont, in command of the Federals in the region, secured the Union gains, along with the vital town of Cairo, where the Ohio and Mississippi rivers join. From this time, Missouri fell into guerilla and partisan warfare. The fighting was often vicious, and neighbors found themselves on opposing sides. In late 1863, Confederate cavalry leader Joseph O. “Jo” Shelby led a raid of 600 men out of Arkansas as far north as the Missouri River and back again.

In 1864, long after Vicksburg had fallen to the Federals, Sterling Price headed north into Missouri with 12,000 Confederate horsemen. At first, not many Union forces were arrayed against Price's small army, and it battled garrisons on its way to St. Louis, hoping to seize war materiel there. But Federals along the Mississippi who were meant to be transferred to Sherman in Georgia were instead ordered to St. Louis, and Price had to bypass the city. He then headed west, and two Federal columns set out to crush the little Southern army. The result was the Battle of Westport on October 23 near Kansas City. This was the largest battle in the Missouri; about 30,000 men engaged. Price avoided destruction, then took his army south again. The two forces fought again two days later near Mine Creek, Kansas, and a few days after that at Newtonia, Missouri, before Price took his men back into southern Arkansas.

Arkansas

Like Virginia, Arkansas seceded from the Union only after Fort Sumter demonstrated that the North was not going to let the South go without a fight. In early 1862, Confederate general Earl Van Dorn, using McCulloch and Price's troops, attempted to defeat the Union army that had advanced into Arkansas from Springfield, Missouri, to the north. The result was the Battle of Pea Ridge or Elk Horn Tavern, the largest battle west of the Mississippi. Van Dorn's men included many Cherokee and Creek Indians, and the fierce battle raged for two days before the Union men defeated the Southerners. The battle ensured Missouri would be safe from large Southern armies and helped open the way for the Union advances on Memphis and Vicksburg. Van Dorn's men were sent east to help with campaigns in Mississippi and Tennessee and, as in Missouri, the war in Arkansas fell to irregulars. Northern troops occupied the capital of Little Rock a few months after Grant took Vicksburg in 1863.