Northern Marianas vs Northern Mariana Islands

Northern Marianas and Northern Mariana Islands both are nouns.

Word	Noun	Adjective	Verb	Adverb
Northern Marianas	Yes	No	No	No
Northern Mariana Islands	Yes	No	No	No

As nouns, Northern Marianas and Northern Mariana Islands are synonyms defined as:

Northern Marianas and Northern Mariana Islands: a self-governing territory comprising all of the Mariana Islands except Guam

Northern Marianas (noun)	Northern Mariana Islands (noun)
a self-governing territory comprising all of the Mariana Islands except Guam	a self-governing territory comprising all of the Mariana Islands except Guam