<P> The country's expansion beyond North America began in 1856 with the passage of the Guano Islands Act, causing many small and uninhabited, but economically important, islands in the Pacific Ocean and Caribbean Sea to be claimed . Most of these claims were eventually abandoned due to competing claims from other countries or the guano having been mined out . The Pacific expansion culminated in the overthrow of the Kingdom of Hawaii in 1893 and its annexation in 1898 . Alaska, the last major acquisition in North America, was purchased from Russia in 1867 . </P> <P> Desires for expansion into Spanish territories like Cuba led to the Spanish - American War in 1898, in which the United States gained Guam, Puerto Rico, and the Philippines, and occupied Cuba for several years . While the other two remain territories, the Philippines became independent in 1946, after being a major theater of World War II . Following the war, many islands were entrusted to the U.S. by the United Nations, and while some remain U.S. territories, the Marshall Islands, Federated States of Micronesia, and Palau emerged from the trust territory as independent nations . The last major international change was the acquisition in 1904, and return to Panama in 1979, of the Panama Canal Zone, a region of American sovereignty to build and run the Panama Canal . The final cession of power over the region was made to Panama in 1999 . </P> <P> Regarding internal borders, while territories could shift wildly in size, once established a state has commonly remained within its borders, barring small changes due to river shifts . Only four states - Maine, Kentucky, Vermont, and West Virginia - have been created from land claimed by another state; all of the others were created from territories or directly from acquisitions . The last state of the contiguous United States, commonly called the "lower 48," was admitted in 1912; the fiftieth and most recent state was admitted in 1959 . </P> <Dl> <Dd> <Dl> <Dd> <Dl> <Dd> <Dl> <Dd> Key to map colors </Dd> <Dd> United States states (domestic maps), undisputed area of United States (dispute maps) </Dd> <Dd> United States territories (domestic maps) </Dd> <Dd> disputed area of United States </Dd> <Dd> area changed by event </Dd> </Dl> </Dd> </Dl> </Dd> </Dl> </Dd> </Dl>

When was the last time the us added a state