Tarev, thanks for the link. The info specifically is about CNMI; on one of the maps, there is a line dividing Guam from the rest of the Marianas...politically.
"The Mariana archipelago was initially settled by Chamorro migrants from Southeast Asia around 2000 BC. All the inhabited islands of the archipelago share an ancient history and culture; however, they are now politically separated into the Commonwealth of the Northern Mariana Islands, and the Territory of Guam."
Territory of Guam, meaning United States territory, meaning, everyone born on Guam is a U.S. citizen. Whereas, in Saipan, one can declare their citizenship to be U.S. or not. It's really too complicated to discuss here, but it is very interesting.