Fulton County men fought on both sides in the Civil War, and some were arrested in 1861 as members of the Unionist Peace Society. U.S. troops marched through in April 1862 during the Pea Ridge Campaign. Fulton County Confederates struck a Union town in Missouri in 1863, and U.S. troops raided the county at least three times that year, including an August expedition in which the Spring River Mill at modern-day Mammoth Spring was burned as a guerrilla rendezvous. On May 29, 1864, a wagon train of Unionist refugees was hit at Salem, and eighty were killed. Union troops of the 6th Missouri and 3rd Iowa Cavalry Regiments entered Arkansas on March 10, 1862, to keep Confederate troops led by W.O. Coleman, J. Posey Woodside, and Archibald McFarlane from banding together. After a skirmish on March 12, the two forces collided at a swamp northeast of Salem on the 13th. A four-hour battle began in which the two sides repeatedly charged back and forth on the edge of the swamp before the Union troops fell back to Missouri after suffering 23 casualties and claiming 100 Confederates dead, wounded, and missing.