The correct answer to this open question is the following.
The question refers to places that the United States had gained as a result of its victory over Spain during the Spanish-America War of 1898.
The newly acquired territories after that victory were Guam, the Philippines, and Puerto Rico. And those places initially served the US to establish naval ports that represented strategic military places.
The Spanish-America War started in April 1898, after the Spanish army sank the USS Main ship that was anchored in the shores of la Habana. The war ended in October 1898 with the signing of the Treaty of Paris.