[4] In late 1864, Confederate Major-General Sterling Price invaded the state of Missouri with a cavalry force, attempting to draw Union troops away from the primary theaters of fighting further east.

After several victories early in the campaign, Price's Confederate troops were defeated at the Battle of Westport on October 23 near Kansas City, Missouri.

Union cavalry pursuers under Brigadier General John B. Sanborn skirmished with Price's rearguard that night, but disengaged without participating in heavy combat.

Overnight, Sanborn's troops were reinforced by cavalry under Lieutenant Colonel Frederick W. Benteen, bringing the total Union strength to 3,500.

The battle began early the next morning as Sanborn drove Major General John S. Marmaduke's Confederate rearguard from its position north of the river.

Marmaduke attempted to make a stand at the river crossing, but his position was outflanked by a Union cavalry regiment, forcing him to abandon it.

A rearguard action by Confederate Brigadier General John B. Clark Jr.'s 1,200-man brigade bought Price more time to retreat and disengage.

That evening, the Battle of Marmiton River became the day's third action, after which Price burned his supply train so it no longer slowed the retreat.

After another defeat at the Second Battle of Newtonia on October 28, Price's column retreated to Texas through Arkansas and the Indian Territory.

[8] By the beginning of September 1864, events in the eastern United States, especially the Confederate defeat in the Atlanta campaign, gave incumbent president Abraham Lincoln, who supported continuing the war, an edge in the 1864 United States presidential election over George B. McClellan, who promoted ending the war.

[14] By September 24, Price's column had reached Fredericktown, where he learned that the town of Pilot Knob and the St. Louis & Iron Mountain Railroad were held by Union forces under the command of Brigadier General Thomas Ewing Jr. Price had no interest in allowing an enemy force to operate in the rear of his army while he advanced to St. Louis, so he sent Marmaduke and Fagan's divisions to Pilot Knob; Shelby and his men operated north of the town.

The next day, Price moved against the fort and offered Ewing surrender terms; the latter refused, as he was afraid of being executed for his unpopular issuance of General Order No.

The Confederates suffered at least 800 casualties during the engagement and their morale decreased, leading Price to abandon the attempt against St.

[16] After abandoning the St. Louis thrust, Price's army headed for Jefferson City, although the Confederates were slowed by bringing along a large supply train.

[17] On October 7, the Confederates approached Jefferson City, which was held by about 7,000 men – mostly inexperienced militia – commanded by Brigadier General Egbert Brown.

Faulty Confederate intelligence placed the Union strength at 15,000, and Price, fearing another defeat like Pilot Knob, decided not to attack the city, and began moving his army toward Boonville the next day.

[24][25] Price's army next fought a series of engagements as it moved westwards towards Kansas City, Missouri, culminating in the Battle of Westport on October 23.

Blunt suggested an ambitious flanking movement, but was overruled by Major General Samuel R. Curtis,[29] commander of the Department of Kansas.

[33] With his men fatigued and operating in a thunderstorm, he withdrew most of his line, except for the 6th Missouri State Militia Cavalry, which continued skirmishing throughout the night.

[36] Marmaduke withdrew his main force south of the river, but left a skirmish line on a pair of mounds that were 140 feet (43 m) tall.

[37][43] The Confederate commander facing the two militia cavalry regiments feared being isolated from Marmaduke's main body on the other side of the river, so the mound was abandoned.

[47] Union forces captured 100 Confederate soldiers, as well as two cannons and some wagons, north of the river,[45] including around the Trading Post settlement.

Phelps's orders were not to attack unless reinforced,[56] but he assaulted Clark's line with 200 men from his own unit and the two Missouri State Militia commands anyway.

They attempted to bring more troops to Phelps' support, but Price's wagons had cut up the roads during their retreat, making maneuvers difficult.

[60] By the end of October 25, Price's army was so shattered and demoralized that the historian Albert E. Castel described it as essentially an armed mob.

[64] U.S. Route 69 and Kansas State Highway 52 run through the northern portion of the battlefield, although the landscape is generally free from major development.