As Congressional Reconstruction took hold in 1867, most of the former Confederacy was placed under military jurisdiction, which was lifted in each state as soon as it ratified a constitution that gave black men the vote. Political activity erupted among African Americans, who allied themselves with the white Northerners (derided by Southern whites as "carpetbaggers") who had come South after the war.

These changes amounted to a revolution that touched every level of Southern life. Confederate veterans responded by forming paramilitary organizations and systematically terrorizing black and white opponents. Though most such groups were local in nature, particularly in the early years of Reconstruction, many adopted the varied garb and rituals of the Ku Klux Klan, which first appeared in Tennessee in 1866. Klan attacks wracked the entire South, from Florida to Missouri. Congress responded with the Enforcement Acts, designed to ferret out such groups. The bushwhackers associated with Jesse James were, in essence, one manifestation of this violent resistance by Confederate veterans. They carried out their first train robbery during a wave of federal Ku Klux Klan prosecutions, and witnesses described them as "masked in full Ku-Klux style."