This is a list of United States territorial acquisitions, beginning with American independence. The treaty with the United Kingdom in 1783 defined the original borders of the United States.
Texas Annexation, of 1845: In 1836 the Republic of Texas voted to be annexed by the United States. Despite the fact that Mexican leader Santa Anna warned that annexation 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 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 twenty-eighth state.
The Mexican Cession was a product of the Mexican War and the subsequent Treaty of Guadalupe Hidalgo, signed February 2, 1848. In this treaty, Mexico gave the United States 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.
In the Gadsden Purchase of 1853, United States purchased a strip of land along the Mexican border for $10 million, now in New Mexico and Arizona. This territory was later used for the southern transcontinental railroad.
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.
