Pea Ridge National Military Park preserves the site of an 1862 Civil War battle that gave the Union total control of Missouri and led directly to the federal occupation of Arkansas. During the Battle of Pea Ridge, some 26,000 soldiers clashed during the two-day battle, with Confederates under Gen. Benjamin McCulloch and Union forces under Gen. Samuel R. Curtis.
More information on the battle can be found at National Parks Service site.
A little more detailed information:
Maj. Gen. Samuel R. Curtis, USA
Maj. Gen. Earl Van Dorn, CSA
Casualties were heavy, with roughly 4,600 Confederates falling and 1,400 Northerners.
The Confederates were eager to return to Missouri so that its star on their flag would have real meaning. Meanwhile, Lincoln wanted to hold as many Border States in the Union as possible. The verdict of battle at Wilson's Creek in the summer of 1861 had favored the south, but when General Samuel R. Curtis was appointed he restored Union fortunes. Reinforced, and more active than his predecessor John C. Fremont (a political general if there was one) he'd not only secured Missouri, he'd pushed down into northwest Arkansas.
Here's a link to an account of the battle from local papers at the time of the battle. Here's an excerpt from that site:
In its comprehensive report following the fateful Battle of Pea Ridge, the Cincinnati Times included a preface to the battle recounting the Missouri skirmishes and the movements of Price’s army preceding the battle. That article was reprinted by the Wooster Republican (Wooster, Ohio) on March 27, 1862:
Camp Sigel, Pea Ridge, Benton Co., Ark.
Monday evening, March 10.
First Movement toward Arkansas
Some six weeks ago the first Federal movement was made from Rolla, the present terminus of the Southwestern branch of the Pacific Railway, toward Springfield, at which well known town Sterling Price was then encamped, with a body of Missouri State troops estimated at eight to ten thousand. Immediately after the evacuation of Fremont’s splendid army, Price marched into Springfield and made his headquarters there, declaring, with the huge oaths for which he is remarkable, that he would never again leave it without a fight. Acting Brigadier General Carr left Rolla with some twenty-four hundred cavalry, as an advance, about the 1st of February, followed by several regiments under Gen. Sigel, for the purpose of engaging the troublesome rebel, and driving him out of the State, which for nine or ten months he had kept in perpetual trouble and alarm, retreating and returning to overrun, ravage and destroy.
Price violated his word once more, and before half his own force was collected in the vicinity of Springfield, evacuated the town, marching down the Cassville road toward Bentonville, Ark., and daily expecting reinforcements from McCulloch, McIntosh, Van Dorn and Albert Pike, with two or three thousand Cherokee, Choctaw, Creek and Seminole Indians.
Various skirmishes occurred on the march, between our forces and those of the enemy, and a small engagement near the State line, resulting in the repulse of Price, and his crossing over into Arkansas, followed by our army.