In the mid-19th century, the use of guano (seabird droppings) began to be used as fertilizer to enrich the "exhausted or poor" farmland of old Europe.
Its "harvesting" was done, almost exclusively, in the Chincha Islands (Peru) . This area of the Pacific is populated by producers of guano (gulls, pelicans...) which for years has been accumulating on the island's surface (several meters thick). Peru controlled the production and England its trade. The US remained outside the direct control of the guano and, therefore, had to import it from England at very high costs.
Logically, the Chincha Islands were not the only place of "collection", many other Pacific islands were also "potential producers" of the precious fertilizer. In 1856, to reduce costs and not depend on imports, the United States Congress approved the Guano Islands Act , authorizing United States citizens to take possession of islands with guano deposits:
When any citizen of the United States discovers a deposit of guano on any island, rock, or cay, not within the lawful jurisdiction of any other government, and not occupied by citizens of any other government, and peacefully takes possession of, and occupies, whether island, rock, or cay, may, at the discretion of the President, be considered to belong to the United States.
More than 100 "guano deposits" were claimed as American under this law (today, several of them remain under American rule). So, we can assure you that bird shit was "responsible" for Yankee imperialism.
Source:Great Unknown Episodes in History – Joseph Cummins.