During the American Civil War, groups of so-called “partisan rangers” engaged in bloody campaigns of guerilla attacks, raiding and psychological warfare against rival military units and civilians. These units had tenuous ties to the regular Confederate and Union Armies and were led by men who often operated outside the recognized rules of warfare.

William C. Quantrlll

One of the Civil War’s most infamous figures, William Quantrill spent most of his early life as a schoolteacher and gambler. Shortly after war broke out, Quantrill assembled a ragtag band of guerillas and began harassing and killing Union forces and sympathizers along the Missouri-Kansas border. His exploits earned him the rank of captain from the Confederate Army, but he was also labeled an outlaw by the Union, which viewed his unconventional tactics as illegal and even murderous.

Did you know? Many infamous outlaws of the American West started out as members of guerilla units during the Civil War. Bank robbers like Jesse James, Frank James and Cole Younger got their taste for violence while riding with Confederate raider William Quantrill, and outlaw organizations like the Mason Henry Gang first sprang up in California as Confederate bushwhacker groups. The tactics they learned from guerilla warfare—including raiding, robbery and evading capture—would later prove invaluable to these men during their outlaw careers.

Quantrill’s most brutal attack came in 1863 when he led 450 guerillas on a raid on the Union stronghold of Lawrence, Kansas. In one of the war’s great atrocities, Quantrill and his men burned the town and executed some 200 men. Union forces responded by burning four nearby Missouri counties and driving the citizens off their land. In the confusion that followed, Quantrill’s raiders disbanded and formed smaller guerilla units in Texas and Oklahoma. His forces now weakened, Quantrill continued to operate outside of the Confederate Army, which had withdrawn support following his attack on Lawrence. In 1864 Quantrill briefly assembled a band of soldiers with the intention of riding east and assassinating President Abraham Lincoln, but he abandoned the idea after recognizing the strength of Union defenses. Undeterred, Quantrill continued his bloody raids against Union troops well into 1865, when he was killed in Kentucky after suffering a gunshot wound to the chest.

William T. Anderson

Later known as “Bloody Bill” because of his cold-blooded acts against Union soldiers, William T. Anderson entered the Civil War with a well-established outlaw reputation, having already murdered a judge who had killed his father over accusations of horse theft. Known for his brash behavior and piercing eyes, Anderson took up with William Quantrill’s raiders in 1863 and soon began leading attacks against Union forces. When one of his sisters was captured by U.S. soldiers and then killed in an accidental building collapse, Anderson’s dislike for the Union intensified into pathological hatred. He is known to have personally executed several people during William Quantrill’s raid on Lawrence, Kansas, and his unit’s savage tactics reportedly included cutting off enemies’ ears, decapitation and scalping.

In 1864, Anderson’s band—which included famed outlaw Jesse James—attacked a train in Centralia, Missouri, and butchered 22 unarmed Union soldiers. When Union troops were sent in pursuit, Anderson’s outfit—dressed in stolen Federal uniforms—ambushed them and slaughtered another 120 men. Desperate to put a stop to Anderson’s bloodshed, the Union army eventually raised a small militia to hunt him down. In October of 1864, Anderson’s unit was trapped and outnumbered in Missouri, and “Bloody Bill” was killed when he tried to charge the Union troops.

James H. Lane

James Lane was one of the most famous members of the “Jayhawkers,” a group of pro-Union partisans who operated in Kansas before and during the Civil War. A career politician, Lane was elected as one of Kansas’ first U.S. senators in 1861, but he quickly left the safety of Washington, D.C., and returned to the field. There, he organized fighting units to help combat Confederate bushwhackers who were terrorizing the Missouri-Kansas border.

Known as the “Grim Chieftain,” Lane was as calculating a military leader as he was a politician. In 1861 he orchestrated the sacking of Osceola, Missouri, in which the town was burned and nine residents were executed. The attack—which was not authorized by the Union—drew the ire of Confederate guerilla leaders like William Quantrill, who began to target Lane in raids on Union positions. Worried that Lane’s activities were only serving to galvanize the opposition, in 1862 the Union canceled his command. Lane continued to play a vital role in the war effort and later made history when he independently organized the 1st Kansas Volunteer Infantry, the first unit of black soldiers to serve in combat during the Civil War.

John Singleton Mosby

One of the Civil War’s legendary figures, John Mosby was a Confederate colonel whose “hit and run” style of warfare earned him the nickname “the Gray Ghost.” Mosby first entered the war as a private and soon impressed his superiors with his skill at gathering intelligence on Union troop movements. In 1863 J.E.B. Stuart and Robert E. Lee gave Mosby command of a small cavalry unit and unleashed him in central Virginia, where he began tormenting Union positions. A true guerilla force, Mosby’s small posse was known for carrying out blistering attacks on Union outfits and destroying rail lines and bridges before scattering into the woods and blending with the civilian population.

Rather than meeting their enemies in open battle, Mosby’s unit would often slip behind Union lines under cover of darkness and capture soldiers and supplies. In one infamous raid in Fairfax County, Virginia, Mosby’s Rangers crept around Union defenses and proceeded to capture 30 soldiers, 50 horses and several officers without ever firing a shot. According to his memoirs, Mosby personally captured General Edwin H. Stoughton by waking him from his bed with a slap to the back. Mosby continued to operate with impunity in Virginia until the end of the war; the regions he haunted became known as “Mosby’s Confederacy.” When Robert E. Lee surrendered in 1865, Mosby disbanded his unit and returned to civilian life. In a startling move that proved controversial in the South, he went on to join Lincoln’s Republican party and serve in Ulysses S. Grant’s presidential administration as the United States consul to Hong Kong.

Charles Jennison

An ardent abolitionist, Charles Jennison first gained notoriety in the late 1850s as a prominent “Jayhawker”—the moniker assigned to a collection of militant antislavery guerillas in Kansas. At the outset of the Civil War, Jennison organized a small Union force and began waging war on Confederate bushwhackers in Missouri. As ruthless as he was principled, Jennison adopted a “scorched earth” policy of warfare that included razing and looting homesteads that appeared to support Confederate guerillas.

By 1862 Jennison’s attacks had become increasingly indiscriminate—his men were known to rob and gun down Union as well as Confederate sympathizers—and martial law was declared in Kansas. Jennison briefly retired after this controversial period, but he would return to the war in 1863 following William Quantrill’s raid on Lawrence, Kansas. He served until the end of the conflict, at which point he was court-martialed for plundering and discharged from the army. He left military service with a polarizing reputation but went on to serve for several years in the Kansas state legislature.

John McNeill

Along with John Mosby, John McNeill was one of the most effective Confederate guerillas on the Civil War’s eastern front. A native of modern-day West Virginia, he was the leader of McNeill’s Rangers, a small force of roughly 200 men that used guerilla tactics to wreak havoc on Union operations in western Virginia.