Civil War

According to historian Shelby Foote, the American Civil War was actually a rebellion rather than a civil war, with a group of states attempting to secede from the United States and form an independent nation, the Confederate States of America. As such, the war began in late December 1860 with the secession of South Carolina from the United States. South Carolina was followed by 10 other southern states over the course of the next 4 months. Open hostilities between the newly formed Confederate States of America and the United States are generally regarded to have begun on April 12, 1861, with the bombardment of Fort Sumter in Charleston Harbor—a federal property the United States had refused to surrender to the South Carolina authorities. The war is generally considered to have ended with the surrender of Robert E. Lee’s Army of Northern Virginia some 4 years later on April 9, 1865. In actuality, according to historian Jay Monaghan, the war may be said to have begun with the so-called border war along the Kansas and Missouri state lines during the mid-1850s. The war did not end with Lee’s surrender as the other southern armies did not surrender until mid-1865; if one considers the depredations of the Ku Klux Klan and other groups of discharged Confederate soldiers as a guerilla war against the United States, the war did not end until about 1870, in which case the war could be considered to have occurred in three phases, all of which involved spying and surveillance in one form or another.

The Civil War was fought in three major theaters and four minor theaters, with a great deal of spying and intrigue occurring in Europe, Cuba, and the British Caribbean colonies. Northeastern Virginia, including the Shenandoah Valley, has been the focus of generations of historians, and thus the focus of more casual consumers of history, with numerous major battles having been fought along a roughly north-south line between Washington, D.C., and Richmond, Virginia. Other major battles were fought along a line from central and eastern Tennessee into Georgia (leading to the Union Army general William Tecumseh Sherman’s March to the Sea) and along the line east of the Mississippi River from Memphis toward the south. Battles were also fought in Missouri, Arkansas, and Louisiana (referred to simply as the trans-Mississippi) and even from Texas into the New Mexico Territory.

Prelude to the War

In 1854, the Kansas-Nebraska Act became law, allowing for a territory to become free or slave at the will of the majority of voters in the territory. This immediately touched off vicious battles in northeastern Kansas and northwestern Missouri. The battles in this border war could be best described as rival guerrilla bands or perhaps even gangs raiding and counterraiding, attacking individuals, homesteads, newspaper offices, and even churches. Selection and location of targets was largely based on a widespread informant system cultivated by rival forces, with neighbors on opposing sides of the slavery issue secretly providing information to their allies in the armed bands. Missteps by informants brought summary death sentences, perhaps best exemplified by a not yet famous abolitionist named John Brown in the Pottawatomie Massacre of May 24, 1856, when a band led by Brown murdered five men believed to have provided information and other support to a proslavery group that had ransacked Lawrence, Kansas, a few days earlier. Such retaliatory acts on a smaller scale were not uncommon along the border during the war years and beyond.

The War Begins

In March 1861, as the newly elected president Abraham Lincoln prepared to travel from his Springfield, Illinois, home to Washington, D.C., for his inauguration, he was contacted through an intermediary by Allen Pinkerton, who was perhaps the first famous private detective in America. Pinkerton advised Lincoln that his agents had infiltrated a group of southern radicals in Baltimore, Maryland, who had sworn to assassinate Lincoln as he was en route to Washington. During the final stage of his journey, Lincoln switched trains and was disguised and personally guarded by Pinkerton as well as several agents. Whether the plot existed in fact or not has never been entirely determined; Lincoln later complained that he had been duped and made to look foolish entering Washington, D.C., under Pinkerton’s tutelage. Despite Lincoln’s later dissatisfaction with Pinkerton, Pinkerton and many of his agents found themselves on the federal payroll as the forerunners of future police intelligence divisions (called, during the Civil War, the Secret Service, which was a term loosely applied to all northern spies; such spies were said to be “on secret service”) and Army intelligence and counterintelligence units.

By April 1861, both sides had developed spy networks with Washington, D.C., and Richmond, Virginia, which became centers of spying, as well as St. Louis, Missouri, the key to much of the freight and passenger traffic on the Mississippi River and the site of a major federal arsenal and Jefferson Barracks, the largest fort west of the Mississippi at the time. Washington and Richmond, as capital cities, were hubs of information for military strength, troop movements, and purely civil government operations. St. Louis was a hub of communications for the middle border states and the west, as well as the chief source of supply of firearms and munitions for western operations of both sides. In all three cities, “outed” spies, and often mere sympathizers, were placed in what would now be referred to as preventive detention. To assist the federal government in ending Confederate espionage, as well as more generally to put down the rebellion, Lincoln invoked the constitutional provision for suspension of habeas corpus in the event of invasion or insurrection. Suspected spies were arrested and jailed, often on uncorroborated informant testimony, and held without being formally charged.

Other than the Pinkertons, whose information provided to northern generals operating in northeastern Virginia soon came to strain credulity, neither side had an organized intelligence service recognizable today. Commanders in each theater were responsible for their own intelligence gathering, and often this duty fell to low-level, local commanders, with no real attempt to centralize or coordinate information collection or correlation for strategic operations. Thus, a general in Virginia hearing of troop movements to Tennessee had little ability or incentive to communicate the information to his counterpart in Tennessee, quickly or at all. Because of the nature of military science at the time of the Civil War, spying and surveillance were often done by unpaid persons with no official status or training. Due to the nature of the war itself, sometimes quite literally brother against brother, spies and other informants were sometimes motivated by patriotism (a motive often romantically attributed to southern women), by vengeance, or by some form of payment; such informants gave inaccurate or outdated information as often as intelligence of value.

Allan Pinkerton and His Agents

Pinkerton was a noted Chicago detective who in 1850 formed a private investigations firm eventually named the Pinkerton National Detective Agency. Early clients included railroads experiencing theft and labor unrest. Pinkerton and his “operatives” relied on surveillance and undercover work to solve crimes as well as to head off labor troubles. It was his work with the Illinois Central Railroad that brought him into contact with George B. McClellan, then chief engineer for the line. McClellan was instrumental in introducing Pinkerton to Lincoln, and when McClellan, a West Point graduate, was given command of the U.S. troops in Virginia in the fall of 1861, Pinkerton was brought in as Chief of the Intelligence Service, a position he held until McClellan’s removal from command in late 1862. Pinkerton’s wildly exaggerated reports of the size as well as the armament and equipage of Confederate troops has been widely blamed for the failure of McClellan and other Union generals to prosecute the war with sufficient rigor to accomplish early victories. Although no major defeats can directly be blamed on Pinkerton or his agents, they cannot be credited with producing any victories.

Lafayette Baker

Lafayette Baker functioned as an undercover agent for the Union during early 1861 and was given an army commission as a reward. He was made provost marshall of Washington, D.C., in September 1862 and, replacing Pinkerton, ran an effective counterintelligence operation, catching numerous Confederate spies. Following Pinkerton’s methods of surveillance and planting undercover agents, he also began tapping military and civilian telegraph lines. His efficiency may have led to his undoing as intercepted telegraph messages suggested the corruption of a cabinet member. This led to his reassignment to New York City, a city of ethnic unrest and southern sympathy, in late 1863. In April 1865, he was assigned to catch the conspirators in the Lincoln assassination, a mission that proved successful.

Other than the discussed formal operations in the eastern theater of the war, Union generals were responsible for developing their own intelligence. They relied on local, paid informants as well as their own men working undercover. In the Confederacy, the Army Signal Corps developed its own Secret Service Bureau, which operated a network of spies in Washington, D.C., which included an 1840 graduate of West Point named Thomas Jordan and the infamous Rose O’Neal Greenhow, a wealthy widow whose social connections included cabinet members and congressmen.

Women Spies

Greenhow began operating under the direction of Jordan, perhaps as early as the fall of 1860. Using a system of couriers, she sent critical information regarding Union troop movements to Confederate General P. G. T. Beauregard, which may have been instrumental in that general’s victory at First Manassas (called First Bull Run by the Union) in July 1861. She was placed under house arrest in August 1861 but continued to ply the trade of spymaster until her imprisonment in 1862. She was eventually released and sent to Richmond, Virginia. After her arrival in Richmond, Confederate President Jefferson Davis made her a diplomatic courier to Europe, where she continued both an active social life and running an espionage operation. In October 1864, she drowned while trying to run the Union Naval Blockade of Wilmington, North Carolina.

Another well-known female spy for the Confederacy was Belle Boyd of Front Royal, Virginia, in the Shenandoah Valley. Boyd assisted her family in running a hotel in that city and, perhaps by accident, overheard a council of war between Union General James Shields and his lieutenants, information she passed on to Confederate General Thomas Jonathan “Stonewall” Jackson, which greatly assisted him in his Valley Campaign.

The Union too had female spies, although they have never held the seemingly more romantic and thus more celebrated place of female Confederate spies. Among these was Harriet Tubman, well-known for her role as a conductor on the Underground Railroad, who organized a spy network in South Carolina. Also among these were Pauline Cushman, an actress caught with incriminating papers and saved from being hanged as a spy by the timely arrival of Union troops, and Sarah Edmonds, who worked as a woman or successfully disguised herself as a white man or a black man as the need arose.


Armies of the 19th century relied heavily on scouts, a job that fell most often to cavalry units due to their greater mobility compared with men on foot. Cavalry often worked deep behind enemy lines, raiding and gathering information as they destroyed targets of military value. As the war progressed, scouting duties fell increasingly to regularly enlisted cavalrymen working in enemy territory while wearing captured enemy uniforms or civilian clothing. Union Army Officer George Armstrong Custer, in particular, used such men during the final retreat of Lee’s army during March to April 1865. If captured, these men faced immediate hanging because such operations were considered contrary to the rules of war. In the Border States, warfare most often took the form of guerilla operations, with apparently peaceful civilians spying and supplying guerilla bands with information on military targets and who among their neighbors were on the other side.


Civil War spying was a haphazard affair, enjoying mostly local successes and not many of these. Spying operations were not organized according to any strategic plan, nor did they operate under any system of centralized control. Part of this was simply due to the state of the art. The United States had little experience with operating spy networks and no plan for integrating intelligence for any type of strategic planning. As a result, commanders in the field most often relied on scouts and local systems for their immediate areas of operations. What was stated earlier about the Pinkerton agents would apply to Civil War espionage in general; it achieved very little that affected the outcome of individual battles, much less the war.

M. George Eichenberg

See also Espionage ; Spies

Further Readings

Adamson, Hans. Rebellion in Missouri, 1861: Nathanial Lyon and His Army of the West. Philadelphia, PA: Chilton, Book Division, 1961.

Axelrod, Alan. The War Between the Spies: A History of Espionage During the American Civil War. New York, NY: Atlantic Monthly Press, 1992.

Fishel, Edwin. The Secret War for the Union: The Untold Story of Military Intelligence in the Civil War. Boston, MA: Houghton Mifflin, 1996.

Foote, Shelbey. The Civil War: A Narrative (Vol. 1). New York, NY: Random House, 1958.

Larson, Rebecca. Blue and Gray Roses of Intrigue. Gettysburg, PA: Thomas, 1993.

Longacre, Edward. Lincoln’s Cavalrymen: A History of the Mounted Forces of the Army of the Potomac, 1861–1865. Mechanicsburg, PA: Stackpole Books, 2000.

Markle, Donald. Spies and Spymasters of the Civil War. New York, NY: Hippocrene Books, 2004.

Monaghan, Jay. Civil War on the Western Border, 1854–1865. Lincoln, NE: Bison Books, 1984.

Nichols, Bruce. Guerilla Warfare in Civil War Missouri, 1862. Jefferson, NC: McFarland, 2004.

Wittenberg, Eric. The Union Cavalry Comes of Age: Hartwood Church to Brandy Station, 1863. Washington, DC: Brassey’s, 2003.