During the mid-19th century, global agriculture underwent a massive revolution driven by a seemingly unglamorous resource: guano, or accumulated sea bird droppings. Exceptionally rich in nitrogen and phosphate, guano served as an unprecedentedly potent agricultural fertilizer that restored depleted soils across Europe and North America. As demand skyrocketed into a frantic guano fever, Peruvian islands with massive prehistoric guano deposits dominated the global monopoly, driving prices sky-high.
Desperate to secure an independent supply for domestic farmers, the United States Congress passed the Guano Islands Act in August 1856. This extraordinary piece of legislation authorized any U. S.
citizen who discovered an unclaimed, uninhabited island containing guano to claim it as American territory. Once the President verified the claim, the island could be occupied using U. S.
military force if necessary. Under this law, American entrepreneurs, sea captains, and opportunists claimed over 100 remote islands, atolls, and reefs across the Pacific Ocean and Caribbean Sea, including Midway Atoll, Baker Island, and Johnston Atoll. Beyond securing agricultural supplies, the law unexpectedly laid the legal groundwork for 19th-century American overseas territorial expansion, transforming remote uninhabited rocks into crucial geopolitical bases that later served as vital military airfields and naval coaling stations during World War II and the Cold War.
To this day, several U. S. Minor Outlying Islands remain official American territories solely because of this 1856 law.