The islands shown on the map were acquired by the United States to function as trading ports and naval bases, and to increase American influence in the Pacific region.
For example, Hawaii was annexed in 1898 by the United States to strengthen the American strategic presence in the Pacific Ocean. The same happened with Guam and the Philippines, obtained after the victory in the war with Spain.
All these islands were acquired with the intention of strengthening the American presence in the Pacific, through the creation of military bases.