 Territory of Guam and the U.S. Commonwealth of the Northern Mariana Islands; Nauru is a fully sovereign nation, coextensive with the island of the same name; and the Republic of the Marshall Islands is coextensive with that island group.Also noteworthy is Wake Island, which is claimed by both the Republic of the Marshall Islands and the United States, the latter having actual possession under immediate administration of the United States Air Force.Human settlement of Micronesia began several millennia ago.