During the mid-nineteenth century, guano—accumulated bird droppings rich in nitrogen and phosphate—became the world's premier agricultural fertilizer. As American farmers faced soil exhaustion, the United States found itself in desperate need of affordable guano supplies, which were heavily monopolized by Peru. In response, Congress enacted the Guano Islands Act of 1856.
This radical legislation empowered any U. S. citizen who discovered a deposit of guano on an unclaimed, uninhabited island, rock, or key to claim it as U.
S. territory. The Act granted the President authority to deploy military force to protect these claims and extended U.
S. criminal jurisdiction to the islands. Over 100 islands, atolls, and reefs were claimed under this law, including Baker Island, Jarvis Island, Midway Atoll, and Howland Island.
While many claims were later abandoned, several remain under American sovereignty today, serving as critical marine national monuments and geopolitical footholds across the Pacific Ocean and Caribbean Sea.