Northern United States vs North

Northern United States and North both are nouns.

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

As nouns, Northern United States and North are synonyms defined as:

Northern United States and North: the region of the United States lying to the north of the Mason-Dixon line

Northern United States (noun)	North (noun)
the region of the United States lying to the north of the Mason-Dixon line	the United States (especially the northern states during the American Civil War)
	the region of the United States lying to the north of the Mason-Dixon line
	British statesman under George III whose policies led to rebellion in the American colonies (1732-1792)