Midwest vs midwestern United States

Midwest and midwestern United States both are nouns.

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

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

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

Other synonyms of Midwest include middle west.

Midwest (noun)	midwestern United States (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)