Union vs United States

Union and United States both are nouns.

Word	Noun	Adjective	Verb	Adverb
Union	Yes	Yes	No	No
United States	Yes	No	No	No

Union (noun)	United States (noun)
the United States (especially the northern states during the American Civil War)	the executive and legislative and judicial branches of the federal government of the United States
	North American republic containing 50 states - 48 conterminous states in North America plus Alaska in northwest North America and the Hawaiian Islands in the Pacific Ocean; achieved independence in 1776

Union (adjective)	United States (adjective)
being of or having to do with the northern United States and those loyal to the Union during the American Civil War