Rio Grande vs United Mexican States

Rio Grande and United Mexican States both are nouns.

Word	Noun	Adjective	Verb	Adverb
Rio Grande	Yes	No	No	No
United Mexican States	Yes	No	No	No

Rio Grande (noun)	United Mexican States (noun)
a North American river; boundary between the United States and Mexico; flows into Gulf of Mexico	a republic in southern North America; became independent from Spain in 1810