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The U.S. empire was built on bird dung

Historians rarely consider ecology in studies of imperialism. They should

Seabirds in Peru stand on a rock covered in guano, a nitrogen-rich natural fertilizer.

Bird poop, like what’s bedecking these rocks along the coast of Peru, has historically been a hot commodity. European and U.S. demand for Peru’s nitrogen-rich guano — a natural fertilizer — skyrocketed in the mid-1800s. As Peru’s supply dwindled, the United States claimed ownership over some 100 “guano” islands.

Jens Otte/Getty Images

By Sujata Gupta

In December 1855 and January 1856, a trio of vessels set sail from the United States to Jarvis and Baker islands, coral atolls in the middle of the Pacific Ocean.