United States Civil War vs American Civil War

United States Civil War and American Civil War both are nouns.

Word	Noun	Adjective	Verb	Adverb
United States Civil War	Yes	No	No	No
American Civil War	Yes	No	No	No

As nouns, United States Civil War and American Civil War are synonyms defined as:

United States Civil War and American Civil War: civil war in the United States between the North and the South; 1861-1865

Other synonyms of United States Civil War include War between the States.

United States Civil War (noun)	American Civil War (noun)
civil war in the United States between the North and the South; 1861-1865	civil war in the United States between the North and the South; 1861-1865