United Mexican States vs Mexican capital

United Mexican States and Mexican capital both are nouns.

Word	Noun	Adjective	Verb	Adverb
United Mexican States	Yes	No	No	No
Mexican capital	Yes	No	No	No

United Mexican States (noun)	Mexican capital (noun)
a republic in southern North America; became independent from Spain in 1810	the capital and largest city of Mexico is a political and cultural and commercial and industrial center; one of the world's largest cities