The discovery of Peruvian island seabird guano as a potent agricultural fertilizer started a rush to find more in the Pacific and Caribbean.
Shortly after the Guano Islands Act passed in 1856, the United States and other nations claimed dozens of islands in the Pacific Ocean and Caribbean Sea. None of the guano found ever matched the quality of the nitrate-rich variety from Peru’s Chincha Islands. The Pacific and Caribbean guano did, however, contain quantities of other minerals like phosphate and potassium that were useful for agricultural fertilizer.
Once islands claimed under the act were mined out, most were abandoned, or their rights were sold to other parties hoping to get rich quick. A few are still “unincorporated and unorganized territories” of the United States.