Guano Islands Act
The Guano Islands Act (11 Stat. 119, enacted 18 August 1856, codified at 48 U.S.C. ch. 8 §§ 1411-1419) is federal legislation passed by the U.S. Congress that enables citizens of the U.S. to take possession of islands containing guano deposits. The islands can be located anywhere, so long as they are not occupied and not within the jurisdiction of other governments. It also empowers the President of the United States to use the military to protect such interests and establishes the criminal jurisdiction of the United States.
Whenever any citizen of the United States discovers a deposit of guano on any island, rock, or key, not within the lawful jurisdiction of any other Government, and not occupied by the citizens of any other Government, and takes peaceable possession thereof, and occupies the same, such island, rock, or key may, at the discretion of the President, be considered as appertaining to the United States.—first section of Guano Islands Act
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In the 1840s, guano came to be prized as a source of saltpeter for gunpowder as well as an agricultural fertilizer. The United States began importing in 1843 through New York. By the early 1850's the UK imported over 200,000 t a year, and U.S. imports totaled about 760,000 t.  Congress passed the Guano Islands Act in August of 1856 to take advantage of these deposits sending armed military to intervene. This encouraged American entrepreneurs to search and exploit new guano deposits on tiny islands and reefs in the Caribbean and in the Pacific. The act specifically allows the islands to be considered possessions of the U.S., but it also provided that the U.S. was not obliged to retain possession after the guano was exhausted. However, it did not specify what the status of the territory was after it was abandoned by private U.S. interests. The implication is that it would return to its former status as terra nullius. The guano mania of the 1850s: urged the creation of the 1856 Guano Islands Act, rose prices in an oligopolistic market, rose attempts of price control and created fear of resource exhaustion. 
This is the beginning of the concept of insular areas in U.S. territories. Up to this time, any territory acquired by the U.S. was considered to have become an integral part of the country unless changed by treaty and eventually to have the opportunity to become a state of the Union. With insular areas, land could be held by the federal government without the prospect of its ever becoming a state in the Union.
More than 100 islands have been claimed for the U.S. under the Guano Islands Act. Most are no longer considered United States territory; those remaining under U.S. claim are:
- Baker Island
- French Frigate Shoals (part of Hawaii)
- Howland Island
- Jarvis Island
- Johnston Atoll
- Kingman Reef/Danger Rock
- Midway Atoll
- Navassa Island (claimed by Haiti)
- Palmyra Atoll
- Bajo Nuevo Bank (disputed with Colombia)
- Serranilla Bank (disputed with Colombia)
- Swains Island (part of American Samoa; no evidence that guano was mined)
Unlike some of the other islands claimed under the Guano Act of 1856, but whose ownership was also disputed, a series of events cemented Navassa Island becoming part of the United States. Because of the actions of Haiti due to its own claim to Navassa Island, President James Buchanan issued Executive Orders establishing United States territorial jurisdiction beyond just the Guano Act. The United States Supreme Court in 1890 ruled the Guano Act of 1856 constitutional; and, citing the actions of the Executive Branch, amongst other points in Law, determined Navassa Island as pertaining to the United States. Control of Navassa Island was transferred by the Department of the Interior to the Director of the Office of Insular Affairs under Order No. 3205 on January 16, 1997, both the Department of the Interior, and Insular Affairs, would later grant administration responsibilities to the United States Fish and Wildlife Service under Order No. 3210 on December 3, 1999. Order No 3210 also established a 12 nautical mile territorial sea boundary for the United States around Navassa Island.
In 1964, Leicester Hemingway, brother of author Ernest Hemingway, attempted to establish a country (or more appropriately, a micronation) dubbed the Republic of New Atlantis, on an 8 x 30 foot bamboo raft anchored with an engine block outside the territorial waters of Jamaica, using the Guano Islands Act as part of a claim to sovereignty. His apparent intention was to use the new country as the headquarters for his own International Marine Research Society, with which he planned to further marine research, as well as to protect Jamaican fishing. His claim was never recognized by either the USA or Jamaica, and the raft was destroyed in a storm in 1966.
- List of Guano Island claims
- United States Miscellaneous Pacific Islands
- United States Minor Outlying Islands
- Smil, Vaclav. (2004). Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production. Massachusetts: The MIT Press, pp.42.
- Skaggs & Wines, R. A. (1985). Fertilizer in America. Philadelphia: Temple University Press, pp. 54-70.
- "Acquisition Process of Insular Areas". United States Government, Department of the Interior. Retrieved 2010-05-09.
- Stahr, Walter (2012) Seward:Lincoln's Indispensable Man. New York, Simon and Schuster, Kindle location 2856 of 15675 "several islands first claimed under the guano island law" ISBN 978-1-4391-2794-0.
- Page 213, in Jimmy M. Skaggs (1994), The Great Guano Rush: Entrepreneurs and American Overseas Expansion. ISBN 978-0-312-10316-3.
- Jones v. United States, 137 U. S. 202 (1890).
- Text of U.S. Code, Title 48, Chapter 8
- 34th Congress Statutes at Large
- 43rd Congress Statutes at Large