German-Americans were the largest ethnic contingent to fight for the Union in the American Civil War. More than 200,000 native-born Germans, along with another 250,000 1st-generation German-Americans, served in the Union Army, notably from New York, Wisconsin, and Ohio. Several thousand also fought for the Confederacy. Most German born residents of the Confederacy lived in Louisiana and Texas. Many others were 3rd- and 4th-generation Germans whose ancestors migrated to Virginia and the Carolinas in the 18th and early 19th centuries.

During the American Civil War, the United States Army, the land force that fought to preserve the collective Union of the states, was often referred to as the Union Army, the Grand Army of the Republic, the Federal Army, or the Northern Army. It proved essential to the restoration and preservation of the United States as a working, viable republic.