They served on opposite sides of the American Civil War: Meagher serving with the Union, for which he recruited and commanded the Irish Brigade, and Mitchel allying himself with the South and living there, sending three sons to fight with the Confederacy.
During the American Civil War, Meagher fought for the Union, leading the Irish Brigade, while Mitchel supported the Confederacy, living in the South and sending his sons to fight for the Confederate cause.