Northern United States vs USA

Northern United States and USA both are nouns.

Word	Noun	Adjective	Verb	Adverb
Northern United States	Yes	No	No	No
USA	Yes	No	No	No

Northern United States (noun)	USA (noun)
the region of the United States lying to the north of the Mason-Dixon line	the army of the United States of America; the agency that organizes and trains soldiers for land warfare
	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