The United States (especially the northern states during the American Civil War) WordNet 3.0 & Open English WordNet

During the American Civil War, the United States of America was referred to as the Union, also known colloquially as the North, after eleven Southern slave states seceded to form the Confederate States of America, which was called the Confederacy, also known as the South. Wikipedia

National government of President Abraham Lincoln and 24 states supporting it Wikipedia Disambiguation

U.S. states that were loyal to the U.S. federal government Wikipedia Disambiguation

The federal government of the United States and the states loyal to it during the American Civil War Wikipedia Disambiguation

The United States's national government and the 20 free states and five border slave states during the Civil War Wikidata

Those of the United States that did not secede at the time of the Civil War (of the United States of America). Wiktionary