From Wipkidia

Shortly after the start of the war, Sigel was commissioned colonel of the 3rd Missouri Infantry, a commission dating from May 4, 1861. He recruited and organized an expedition to southwest Missouri, and subsequently fought the Battle of Carthage, where a force of pro-Confederate Missouri militia handed him a setback in a strategically insignificant fight. However, Sigel's defeat did help spark recruitment for the Missouri State Guard and local Confederate forces. Sigel later took part in a skirmish at Dug Springs.

Throughout the summer, President Abraham Lincoln was actively seeking the support of anti-slavery, pro-Unionist immigrants. Sigel, always popular with the German immigrants, was a good candidate to advance this plan. He was promoted to brigadier general on August 7, 1861, to rank from May 17, one of a number of early political generals endorsed by Lincoln.

Sigel served under Brig. Gen. Nathaniel Lyon in the capture of the Confederate Camp Jackson in St. Louis and at the Battle of Wilson's Creek, where his command was routed after making a march around the Confederate camp and attacking from the rear. Sigel conducted the retreat of the army after the death of General Lyon.

Riverside Drive, New York City
His finest performance came on March 8, 1862, at the Battle of Pea Ridge, where he commanded two divisions and personally directed the Union artillery in the defeat of Maj. Gen. Earl Van Dorn on the second day of the battle.

Sigel was promoted to major general on March 21, 1862. He served as a division commander in the Shenandoah Valley and fought unsuccessfully against Maj. Gen. Thomas J. "Stonewall" Jackson, who managed to outwit and defeat the larger Union force in a number of small engagements. He commanded the I Corps in Maj. Gen. John Pope's Army of Virginia at the Second Battle of Bull Run, another Union defeat, where he was wounded in the hand.

Over the winter of 1862–63, Sigel commanded the XI Corps, consisting primarily of German immigrant soldiers, in the Army of the Potomac. During this period, the corps saw no action; it stayed in reserve during the Battle of Fredericksburg. Sigel had developed a reputation as an inept general, but his ability to recruit and motivate German immigrants kept him alive in a politically sensitive position. Many of these soldiers could speak little English beyond "I'm going to fight mit Sigel", which was their proud slogan and which became one of the favorite songs of the war. They were quite disgruntled when Sigel left the corps in February 1863, and was replaced by Maj. Gen. Oliver O. Howard, who had no immigrant affinities. Fortunately for Sigel, the two black marks in the XI Corps' reputation—Chancellorsville and Gettysburg—would occur after he was relieved.

The reason for Sigel's relief is unclear. Some accounts cite failing health; others that he expressed his displeasure at the small size of his corps and asked to be relieved. General-in-chief Henry W. Halleck detested Sigel, and managed to keep him relegated to light duty in eastern Pennsylvania until March 1864. President Lincoln, for political reasons, directed Secretary of War Edwin M. Stanton to place Sigel in command of the new Department of West Virginia.

In his new command, Sigel opened the Valley Campaigns of 1864, launching an invasion of the Shenandoah Valley. He was soundly defeated by Maj. Gen. John C. Breckenridge at the Battle of New Market, on May 15, 1864, which was particularly embarrassing due to the prominent role young cadets from the Virginia Military Institute played in his defeat. After the battle, Sigel was replaced by Maj. Gen. David Hunter. In July, Sigel fought Lt. Gen. Jubal A. Early at Harpers Ferry, but soon afterward was replaced by Albion P. Howe. Sigel spent the rest of the war without an active command.

Francis Sigel