Congressional act of the United States
The Guano Islands Act (11 Stat. 119, enacted August 18, 1856, codified at 48 U.S.C. ch. 8 §§ 1411-1419) is a United States federal law passed by the Congress that enables citizens of the United States to take possession of unclaimed islands containing guano deposits in the name of the United States. The islands can be located anywhere, so long as they are not occupied by citizens of another country and not within the jurisdiction of another government. It also empowers the president to use the military to protect such interests and establishes the criminal jurisdiction of the United States in these territories.
Background.
In the 1840s, guano became a prized agricultural fertilizer and source of saltpeter for gunpowder. 
The U.S. began importing it in 1843 through New York. By the early 1850s, the U.K. imported over 200,000 tons a year, and U.S. imports totaled about 760,000 tons. The "guano mania" of the 1850s led to high prices in an oligopolistic market, government attempts to control prices, fear of resource exhaustion, and eventually the enactment of the "Guano Islands Act of 1856" in August 1856. The Act authorizes U.S. citizens to take possession of unclaimed islands containing guano for the U.S., empowers the President to protect such claims with military intervention, and establishes jurisdiction of criminal offenses under the laws of the United States within the territories, thus claimed. This encouraged American entrepreneurs to search for and exploit new deposits on tiny islands and reefs in the Caribbean and Pacific.
This was the beginning of the concept of insular area in U.S. territories. Up until 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 it ever becoming a state in the Union.
Under the Act, the U.S. gained control of around 94 islands. By 1903, 66 of these islands were recognized as territories of the U.S.
Wording.
 ;templatestyles src="Template:Blockquote/styles.css" / ;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.
Criminal jurisdiction.
Section 6 provides that criminal acts on or adjacent to these territories "shall be deemed committed on the high seas, on board a merchant ship or vessel belonging to the United States; and shall be punished according to the laws of the United States relating to such ships or vessels and offenses on the high seas". The provision was considered and ruled constitutional by the U.S. Supreme Court in "Jones v. United States", 137 U.S. 202 (1890).
Result.
The Act continues to be part of the law of the United States. The most recent Guano Islands Act claim was made in 1997 to Navassa Island. However, the claim was denied because an American court ruled the island was already under American jurisdiction (a claim Haiti disputes).
Claims.
While more than 100 islands have been claimed for the United States under the Guano Islands Act, all but ten have been withdrawn. The Act specifically allows the islands to be considered possessions of the U.S. The Act does not specify the territory's status after private U.S. interests abandon it or the guano is exhausted, creating neither obligation nor prohibition of retaining possession.
, the islands still claimed by the United States under the Act are:
Disputed claims.
A few islands claimed by the United States under the "Guano Act of 1856" are disputed. 
References.
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