U.S. vs midwestern United States

U.S. and midwestern United States both are nouns.

Word	Noun	Adjective	Verb	Adverb
U.S.	Yes	No	No	No
midwestern United States	Yes	No	No	No

U.S. (noun)	midwestern United States (noun)
the executive and legislative and judicial branches of the federal government of the United States	the north central region of the United States (sometimes called the heartland or the breadbasket of America)
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