"In December 1862, Peruvian slave traders landed on Easter Island and captured approximately 1,500 Rapa Nui people, including much of the island's leadership and elite. The raids were brutal, and the kidnapped islanders were transported to the guano islands and plantations on the Peruvian coast. Of these 1,500 individuals, only a small fraction would ever return.Of the roughly 1,500 people taken, it is estimated that fewer than 100 survived to return home. By the mid-19th century, the island's population had been reduced to just a few hundred, down from an estimated 3,000–4,000 before the raids."
The invention of ammonia synthesis from atmospheric N2 via the Haber-Bosch process largely put an end to the guano industy and the slave labor that supported it. There's an excellent book, "The Alchemy of Air" by Thomas Hager that covers this history well: