The Missouri State Guard was commanded by Governor Claiborne F. Jackson himself and numbered over 4,000 soldiers led by a hero of Mexico, Sterling Price, along with 2,000 unarmed troops who did not participate in the battle.

Publicly Jackson tried to stay neutral, but he was suspected by the Union men of secretly preparing the state militia to seize the Federal Arsenal in St. Louis.

Lyon, like many St. Louis Unionists, feared that Governor Jackson would employ the city's secessionist Minutemen paramilitary organization and the local Missouri Volunteer Militia to capture the Arsenal.

Beginning on April 22, 1861, on the orders of President Lincoln, Lyon mustered in four regiments of Federal Missouri Volunteers (mostly former members of Republican Wide Awake marching clubs), issuing them weapons drawn from the Arsenal stocks.

The crisis grew worse when a shipment of Confederate siege artillery arrived at the state Militia encampment, Camp Jackson, on May 8–9, 1861.

The action drew great protests from Missourians, and even representatives of the City of St. Louis petitioned Lincoln for Lyon's dismissal.

After four hours, Lyon abruptly ended the meeting, and Jackson and Price retreated to Jefferson City, ordering railroad bridges burned behind them.

Lyon moved elements of his St. Louis garrison up the Missouri River by steamer to capture the state capital at Jefferson City.

Learning that Sigel had encamped at Carthage, Governor Jackson took command and made plans to attack the smaller but better armed Union force.

Sigel's men provided an impressive display as they formed a line of battle and moved within 800 yards of the State Guard troops.

Jackson and the State Guard then chased after Sigel's brigade, engaging them in battle as they pushed them 10 miles southward until they reached the outskirts of Carthage.

The battle was a strategic victory by the Missouri State Guard in large part owing to new tactics introduced on the battlefield by independent partisan rangers serving with Captain Jo Shelby.

Serving at the vanguard of Governor Jackson's army, a band of 150 independent partisan rangers were under the command of Captain Jo Shelby, a Missouri farmer.