Territory ceded by Spain to the U.S. in 1898 (4)
I believe the answer is:
guam
(Other definitions for guam that I've seen before include "North Pacific island, base for the US navy and air force" , "Largest of the Mariana Islands" , "NW Pacific island with large US base" , "US unincorporated territory in the western Pacific" , "US island east of the Philippines" .)