In 1804 geographer Alexander von Humboldt brought samples of Peruvian guano to Europe. This type of guano, decades later, would become one of the most highly prized natural resources in the world. In the 1840s, guano was prized as an agricultural fertilizer. The primary source for guano at the time were the Chincha Islands off of the Peruvian Coast. The guano mining operations of Peru kept the country from becoming bankrupt although American, British, and European farmers resented paying the high costs of Peruvian bird droppings.
Fish-eating sea birds, most notably the white-breasted cormorant, have been depositing their seafood-based droppings off the coast of Peru for thousands of years. The guano of Peru is most notable due to the limited precipitation in the region. Guano is dropped and dries quickly, preserving the chemicals that make it useful for fertilizer. Is moist environments, the nitrates evaporate, making the deposits less rich than those of Peru.
On some islands, as much as one hundred and fifty feet of guano had accumulated by the time the deposits were discovered. The western companies that exploited the islands for their guano also exploited Chinese and other laborers to mine the guano for use as fertilizer.
In 1855, the U.S. government received reports that Baker Island in the Pacific Ocean was also rich with guano deposits. Congress took action and on August 18, 1856 the Guano Island Act was passed. It empowered American citizens to take possession of any island or rock or key with guano deposits not under the control of a foreign government. The full act also allowed the President to utilize the military to protect the interests of the discoverer.
Additionally, while the act allowed the President to annex a guano island or rock or key, it did not require that the United States retain possession of a guano-filled locale. This was a difference in law as typically annexations require a treaty to give up possession of a territory - thus the Guano Island Act set out to differentiate guano islands from other annexed territories.
The first annexation was that of Baker Island on May 1, 1857. A Baltimore newspaper called the island "a new El Dorado" due to the value of guano as a agricultural resource and the lower cost with which guano could be had by American farmers. Over the next few decades, dozens of rocks and islands were annexed into the United States due to their guano deposits and the Guano Island Act. These included Jarvis Island, Howland Island, Christmas Island, Johnson Atoll, Navassa Island, and Midway Island.
The industrial ideals of the late nineteenth century did not provide for conservation of wildlife so the exploitation of the guano islands resulted in the loss of millions of sea birds, making the guano on the islands a non-renewable resource. Nonetheless, the invention of chemical fertilizers dramatically reduced the need for guano as fertilizer.