Anthony/Brady.   In 1861, the Civil War began and Slough immediately began recruiting for the federal army. Colorado Governor William Gilpin appointed him as a captain of the 1st Colorado "Pike's Peakers" Infantry Regiment. Members of his regiment were initially skeptical of his loyalty to the Union due to his association with the Democratic Party. In August 1861, Slough was commissioned colonel in command of the regiment. In 1862, a Confederate army was invading the New Mexico Territory, had defeated Col. Edward R. S. Canby's troops at the Battle of Valverde, and captured Albuquerque and the capital of Santa Fe. Coming to the aid of the Union forces in New Mexico, Slough marched his regiment to Fort Union and, as the senior ranking officer, assumed command of the post and its New Mexico Volunteers.A Confederate force under Lt. Col. William Read Scurry was moving to capture Fort Union. Col. Slough marched his regiment toward Glorieta Pass to intercept Scurry. On March 26, 1862, an advanced unit met the Confederates at Apache Canyon, an inconclusive skirmish ensued. Two days later, on March 28, the armies met at Pigeon's Ranch on the Santa Fe Trail below Glorieta Pass. Slough and Scurry fought an initially indecisive action at the Battle of Glorieta Pass. The Texans were pushing the Coloradans back, but the battle was turned to a victory for the Union after Slough sent Major John M. Chivington on a flank attack which destroyed the Confederate's supply train. The battle was considered a Union strategic victory but a Confederate tactical victory. Slough's regiment had stopped the advance of the Confederates, who soon abandoned New Mexico and retreated back to Texas.Following the battle, Slough received direct orders from Canby to remain at Fort Union. Though dated and sent before the battle while the Confederate army divided Canby and Slough's communication line, the order has been debated as confirmation or not that Slough had disobeyed Canby's orders by leaving Fort Union in the first place. Slough met with Canby, determined the war in New Mexico was over, resigned his commission, and immediately headed to the Eastern theater. At the first anniversary after the Battle of Glorieta Pass, his former Colorado troops sent him a gold inlaid sword as thanks for making the rag tag volunteers into a fighting force. In response, Slough wrote: “Remember the holy character of the cause in which you are engaged. Remember that you are American soldiers, battling in the cause of universal freedom.”[1]Through his wife's McLean family ties (the chief justice of the U. S. Supreme Court was a relative), Slough went to Washington, D.C., where he was given command of a brigade in the Shenandoah Valley during Stonewall Jackson's Valley Campaign of 1862. His forces were stationed at Harpers Ferry and saw little action. He was appointed brigadier general of volunteers of August 25, 1862, and became the military governor of Alexandria, Virginia. For the rest of the war, he commanded the District of Alexandria. In December 1862, he sat on the court-martial that convicted Maj. Gen. Fitz John Porter of disobedience and misconduct.