At the start of the Civil War, Sigel volunteered to support Abraham Lincoln and the Union cause. Because of his military experience, he was given command of the Third Missouri Infantry. He recruited many German-Americans to the Union cause with the slogan, "I goes to fight mit Sigel." His commission as Colonel held a date of rank of May 4, 1861. Because he was a key figure in recruiting immigrants to the Union army, President Lincoln had him promoted to Brigadier general two weeks later.