With the Emperor's permission, Shelby formed a colony of Confederate exiles in Mexico until the defeat of the French, then abandoned the operation.

[2] When the Kansas-Nebraska Act of 1854 was passed, the New England Emigrant Aid Company paid for Northern abolitionists to move to Kansas.

[4] Shelby's leadership in the Missouri–Kansas border war damaged his business ventures and partnership with his stepbrother, Henry Howard Gratz.

[6] 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.

[7] 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.

[8] 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.

[9] Reassigned to Clarendon, Arkansas, Shelby succeeded in capturing a Union tinclad (lightly armored) gunboat, the USS Queen City.

He distinguished himself at the battles of Little Blue River and Westport, and briefly captured many towns from their Union garrisons, including Potosi, Boonville, Waverly, Stockton, Lexington, and California, Missouri.

A later verse appended to the post-war Confederate anthem "The Unreconstructed Rebel" commemorates the defiance of Shelby and his men: I won't be reconstructed, I'm better now than then.

Maximilian declined to accept the ex-Confederates into his armed forces, but he did grant them land for the New Virginia Colony, an American settlement in Mexico near Córdoba, Veracruz.

Under other conditions, he would have been one of the best in the world.”[19][21] Shelby Park in Eagle Pass, Texas was named after him, which historian Jeremi Suri described as ironic because it militarizes the assertion of power like the original treason in the Confederacy.

Shelby and his men buried their Battle Flags on the North bank of the Rio Grande before entering Mexico according to the famous Texas Ranger and Cavalry Officer Colonel Alexander Watkins Terrell who was present at the crossing.