American Civil War: Confederate spy Belle Boyd is arrested by Union troops and detained at the Old Capitol Prison in Washington, D.C.

The American Civil War was a civil war in the United States between the Union and the Confederacy, which was formed in 1861 by states that had seceded from the Union. The central conflict leading to war was a dispute over whether slavery should be permitted to expand into the western territories, leading to more slave states, or be prohibited from doing so, which many believed would place slavery on a course of ultimate extinction.

The Confederate States of America (CSA), also known as the Confederate States (C.S.), the Confederacy, or the South, was an unrecognized breakaway republic in the Southern United States from 1861 to 1865. It comprised eleven U.S. states that declared secession: South Carolina, Mississippi, Florida, Alabama, Georgia, Louisiana, Texas, Virginia, Arkansas, Tennessee, and North Carolina. These states fought against the United States during the American Civil War.

Maria Isabella Boyd, best known as Belle Boyd was a Confederate spy in the American Civil War. She operated from her father's hotel in Front Royal, Virginia, and provided valuable information to Confederate General Stonewall Jackson in 1862.

The Union was the central government of the United States during the American Civil War. Its civilian and military forces resisted the Confederacy's attempt to secede following the election of Abraham Lincoln as president of the United States. Lincoln's administration asserted the permanency of the federal government and the continuity of the United States Constitution.