midwestern United States vs Midwest

midwestern United States and Midwest both are nouns.

Word	Noun	Adjective	Verb	Adverb
midwestern United States	Yes	No	No	No
Midwest	Yes	No	No	No

As nouns, midwestern United States and Midwest are synonyms defined as:

midwestern United States and Midwest: the north central region of the United States (sometimes called the heartland or the breadbasket of America)

Other synonyms of midwestern United States include middle west.

midwestern United States (noun)	Midwest (noun)
the north central region of the United States (sometimes called the heartland or the breadbasket of America)	the north central region of the United States (sometimes called the heartland or the breadbasket of America)