The United States acquired Puerto Rico through the Treaty of Paris following the end of the Spanish–American War.

The U.S. Virgin Islands was sold to the United States by Denmark in 1916.

U.S. territories in the Pacific were acquired in various ways. Following World War II, the Northern Marianas, Federated States of Micronesia, Republic of the Marshall Islands, and the Republic of Palau were all made part of the Trust Territories of the Pacific; this was an agreement administered by the United Nations and governed by the United States.

The territory of Guam was acquired through the Treaty of Paris following the end of the Spanish-American War.

American Samoa was originally a part of the Samoan Islands but was acquired through a treaty with Germany, a rival world power in 1899.