Territorial acquisition is the acquiring of territory or land along with all it contains through various means, including war, treaties and purchase. After the American Revolution, the 13 American colonies sought territorial acquisitions in an effort to expand boundaries.
After many territorial acquisitions, the United States reached its current 2014 size in 1917. Guam was a territorial acquisition of the U.S. in 1898 under the Treaty of Paris. Guam was subsequently captured by Japan in 1941, but the U.S. regained it as a territory in 1944. Some territorial acquisitions are no longer under U.S. control, such as the Federated States of Micronesia, which was a United Nations Trust Territory under U.S. administration after World War II, but became an independent country in 1986, according to National Atlas.