The American Civil War began in 1861, when James was eighteen years old. The secessionists in Missouri, including Governor Claiborne Fox Jackson, attempted to drive the Union army out of the state but were eventually defeated. The James family was from the heavily Confederate western portion of the state. On September 13, 1861, the Missouri State Guard, including private Frank James, besieged Lexington, Missouri. James fell ill and was left behind when the Confederate forces retreated. He surrendered to the Union troops, was paroled, and was allowed to return home. On his arrival, however, he was arrested by the local pro-Union militia and was forced to sign an oath of allegiance to the Union.