United States territorial acquisitions

Notes and caveats

Note that this list primarily concerns land acquired from other nation-states; the numerous territorial acquisitions from American Indians are not listed here. One perspective on this state of affairs is that the land was claimed as the territory of one European colonial power or the other, but it was owned by the Native peoples who resided there, creating a tiered system of possession. (For example, under this standard, Kansa Indians would be considered French nationals pre-1803, and American nationals post-1803.) For an in-depth exploration of Native American land cessions, researchers may refer to Eighteenth Annual Report of the Bureau of American Ethnology to the Secretary of the Smithsonian Institution, 1896-1897 by Charles C. Royce, which can be viewed online at the Library of Congress' American Memory Website.

The 1783 Treaty of Paris with Great Britain defined the original borders of the United States. Due to ambiguities in the treaty, the ownership of Machias Seal Island and North Rock remain disputed between the U.S. and Canada; other original territorial ambiguities (including the Northeastern Boundary Dispute and the disputed Indian Stream territory) were resolved by the Webster-Ashburton Treaty in 1842.

The Louisiana Purchase, completed 1803, was negotiated by Robert Livingston during the presidency of Thomas Jefferson; the territory was acquired from France. A small portion of this land was ceded to Great Britain in 1818 in exchange for the Red River Basin. More of this land was ceded to Spain in 1819 with the Florida Purchase, but was later reacquired through Texas annexation and Mexican Cession.

West Florida was declared by President James Madison to be a U.S. possession in 1810.

Red River Basin, acquired in 1818 by treaty from Great Britain, i.e. Anglo-American Convention of 1818.

The Adams-Onís Treaty of 1819 with Spain resulted in the cession of East Florida and the Sabine Free State and the surrender of any claims to the Oregon Country. Article II of the treaty, when properly surveyed, resulted in the acquisition of a small part of central Colorado.

Texas Annexation of 1845: In 1836 the Republic of Texas voted to be annexed by the United States. Despite the fact that Mexican leader Antonio López de Santa Anna warned that this would be "equivalent to a declaration of war against the Mexican Republic," President John Tyler signed a treaty of annexation with Texas in April 1844, causing the Mexican-American War. After James Polk, a strong supporter of territorial expansion, won the presidency, but before he took office, Congress approved the annexation of Texas on February 28, 1845. On December 29, 1845, Texas became the 28th state.

Oregon Country, the area of North America west of the Rockies to the Pacific, was jointly controlled by the U.S. and Great Britain following the Anglo-American Convention of 1818 until 1846 when the Oregon Treaty divided the territory at the 49th parallel (see Oregon boundary dispute). The San Juan Islands were claimed and jointly occupied by the U.S. and Great Britain from 1846-1872 due to ambiguities in the treaty (see Northwestern Boundary Dispute). Arbitration led to the sole US possession of the San Juan Islands since 1872.

Mexican Cession lands were a product of the Mexican-American War and the subsequent Treaty of Guadalupe Hidalgo, signed February 2, 1848. In this treaty, Mexico gave the U.S. parts of what is Texas, Colorado, Arizona, New Mexico and Wyoming, and the whole of California, Nevada and Utah and recognized the Rio Grande as Texas' Southern border. The United States paid Mexico $15 million. In addition, the United States agreed to pay claims made by American citizens against Mexico, which amounted to more than $3 million.

Gadsden Purchase of 1853, United States purchased a strip of land along the U.S.-Mexico border for $10 million, now in New Mexico and Arizona. This territory was later used for the southern transcontinental railroad.

The Guano Islands Act of 1856 provided for U.S. claims to unoccupied islands. Baker Island, Howland Island, and Navassa Island were annexed in under its provisions in 1857. Today ownership of Navassa is disputed between the U.S. and Haiti. Johnston Atoll was claimed by the US and Hawaii in 1858; the US claim became undisputed in 1898 after the annexation of Hawaii. Midway Atoll was discovered and claimed in 1859 and formally annexed 1867. Kingman Reef was annexed in 1922.

Chamizal from Mexico from 1852-1873 due to course change of the Rio Grande River. The territory was mostly retroceded to Mexico by treaty in 1963.

Hawaii, annexed 1898 upon the request of a government made up primarily of American and European businessmen who had overthrown the Kingdom of Hawaii. With Hawaii came the Palmyra Atoll which had been annexed by the U.S. in 1859 but later abandoned, then later claimed by Hawaii.

Puerto Rico, Guam and the Philippines, annexed from Spain after the Spanish-American War in 1898 for $20 million under the Treaty of Paris. The Philippines became an independent nation in 1946.

Wake Island, annexed in 1899 (Claim currently disputed by the Marshall Islands)

Tutuila Island and Aunuu Island ceded by their chiefs in 1900, then added to American Samoa.

U.S. Virgin Islands, bought from the Danish Crown for $25 million on January 17, 1917 during the First World War. Virgin Islands inhabitants became American citizens in 1927.

Swains Island, annexed in 1925 (occupied since 1856), then added to American Samoa. (Claim currently disputed by Tokelau).

Jarvis Island, reclaimed in 1935, previously annexed in 1858, but abandoned in 1879.

Marshall Islands, Federated States of Micronesia, Northern Mariana Islands and Palau, occupied by the United States during World War II, formalised under the UN trusteeship system in 1947. Micronesia and the Marshall Islands both achieved independence in 1986 and Palau in 1994, via Compacts of Free Association.

The Boundary Treaty of 1970 transferred 2702.9 acres of Mexican territory to the U.S.. In exchange, the U.S. ceded 2087.87 acres to Mexico, including the town of Rio Rico, Texas.