In the 1840s, guano came to be prized as an agricultural fertilizer and as a source of saltpeter for gunpowder. In 1855, the U.S. learned of rich guano deposits on islands in the Pacific Ocean. Congress passed the Guano Islands Act to take advantage of these deposits.
The act specifically allows the islands to be considered a possession 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.
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 to eventually 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.
The provision of the Act establishing U.S. criminal jurisdiction over such islands was considered and ruled constitutional by the U.S. Supreme Court in Jones v. United States, 137 U.S. 202 (1890).