Following the Confederate attack on Fort Sumter in April 1861, Missouri Governor Claiborne Fox Jackson refused Lincoln's call for volunteers and maneuvered to take the state out of the Union.
The resulting friction between State and Federal militias vying for control of the St. Louis Arsenal led to the Camp Jackson affair and the creation of the pro-secession Missouri State Guard.

Shelby formed the Lafayette County Mounted Rifles for Missouri State Guard service and was elected the company's captain, leading it into battle at Carthage, Wilson's Creek, and Pea Ridge.
In 1862, he was promoted to colonel and authorized to recruit a Confederate cavalry regiment, returning to Lafayette County to do so.
After successfully bringing the regiment safely back to Arkansas, he was given command of a brigade of newly recruited regiments.

In the fall of 1863, Shelby led his "Iron Brigade" of Missouri volunteers on what was at the time the longest cavalry raid of the war, Shelby's Raid.
Between September 22 and November 3, 1863, Shelby's brigade traveled 1,500 miles through Missouri, inflicting over 1,000 casualties on Union forces and capturing or destroying an estimated $2 million worth of federal supplies and property.
He was promoted to brigadier-general on December 15, 1863, following the successful conclusion of his raid.

In 1864, Union General Frederick Steele's failure in the Camden Expedition of March 23 – May 2, 1864 was largely due to Shelby's brilliant and determined harassment, in concert with other Confederate forces.
Steele's men were forced to retreat to Little Rock by the destruction or capture of their supply trains at the Battle of Marks' Mills.
Reassigned to Clarendon, Arkansas, Shelby succeeded in capturing a Union tinclad (lightly armored) gunboat, the USS Queen City.
The gunboat was burned to prevent her recapture.
Shelby then commanded a division during Price's Missouri Expedition.
He distinguished himself at the battles of Little Blue River and Westport, and captured many towns from their Union garrisons, including Potosi, Boonville, Waverly, Stockton, Lexington, and California, Missouri.

After Robert E. Lee's army surrendered in Virginia in April 1865, General Edmund Kirby Smith appointed Shelby a major general on May 10.
The promotion was never formalized, however, due to the collapse of the Confederate government.
Shelby's adjutant at the time was John Newman Edwards, who years later (as editor of the Kansas City Times) was largely responsible for creating the anti-hero legend of Jesse James and his fellow Confederate guerrillas.
Following the Confederate attack on Fort Sumter in April 1861, Missouri Governor Claiborne Fox Jackson refused Lincoln's call for volunteers and maneuvered to take the state out of the Union. The resulting friction between State and Federal militias vying for control of the St. Louis Arsenal led to the Camp Jackson affair and the creation of the pro-secession Missouri State Guard.
Shelby formed the Lafayette County Mounted Rifles for Missouri State Guard service and was elected the company's captain, leading it into battle at Carthage, Wilson's Creek, and Pea Ridge. In 1862, he was promoted to colonel and authorized to recruit a Confederate cavalry regiment, returning to Lafayette County to do so. After successfully bringing the regiment safely back to Arkansas, he was given command of a brigade of newly recruited regiments.
In the fall of 1863, Shelby led his "Iron Brigade" of Missouri volunteers on what was at the time the longest cavalry raid of the war, Shelby's Raid. Between September 22 and November 3, 1863, Shelby's brigade traveled 1,500 miles through Missouri, inflicting over 1,000 casualties on Union forces and capturing or destroying an estimated $2 million worth of federal supplies and property. He was promoted to brigadier-general on December 15, 1863, following the successful conclusion of his raid.
In 1864, Union General Frederick Steele's failure in the Camden Expedition of March 23 – May 2, 1864 was largely due to Shelby's brilliant and determined harassment, in concert with other Confederate forces. Steele's men were forced to retreat to Little Rock by the destruction or capture of their supply trains at the Battle of Marks' Mills. Reassigned to Clarendon, Arkansas, Shelby succeeded in capturing a Union tinclad (lightly armored) gunboat, the USS Queen City. The gunboat was burned to prevent her recapture. Shelby then commanded a division during Price's Missouri Expedition. He distinguished himself at the battles of Little Blue River and Westport, and captured many towns from their Union garrisons, including Potosi, Boonville, Waverly, Stockton, Lexington, and California, Missouri.
After Robert E. Lee's army surrendered in Virginia in April 1865, General Edmund Kirby Smith appointed Shelby a major general on May 10. The promotion was never formalized, however, due to the collapse of the Confederate government. Shelby's adjutant at the time was John Newman Edwards, who years later (as editor of the Kansas City Times) was largely responsible for creating the anti-hero legend of Jesse James and his fellow Confederate guerrillas.
Joseph O. Shelby