Northern Mariana Islands vs Northern Marianas

Northern Mariana Islands and Northern Marianas both are nouns.

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

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

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

Northern Mariana Islands (noun)	Northern Marianas (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