How did bird droppings become valuable enough to influence international politics, national economies, and even wars?

During the 19th century, enormous deposits of guano accumulated on islands along the Pacific coast of South America. Rich in nitrogen and other nutrients, this seemingly ordinary material became one of the world's most valuable fertilizers. Before modern synthetic fertilizers existed, countries desperate to increase agricultural production were willing to pay extraordinary amounts for it.

Peru sat on some of the richest guano deposits in the world, especially around the Chincha Islands. The resulting boom transformed guano into a major source of government revenue, financed international borrowing, and made control of these remote islands strategically important.

But immense value also brought international compe ...