Really sad & epic history here:
In the 1860s the Peruvian slave raids began, as Peruvians were experiencing labor shortages and came to regard the Pacific as a vast source of free labor. Slavers raided islands as far away as Micronesia, but Rapa Nui was much closer and became a prime target.
In December 1862 eight Peruvian ships landed their crewmen and between bribery and outright violence they captured some 1,000 Rapanui, including the king, his son, and the ritual priests (one of the reasons for so many gaps in knowledge of the ancient ways). It has been estimated that 2,000 Rapanui were captured over a period of years. Those who survived to arrive in Peru were poorly treated, overworked, and exposed to diseases. Ninety percent of the Rapa Nui died within one or two years of capture.
Eventually the Bishop of Tahiti caused a public outcry and an embarrassed Peru rounded up the few survivors to return them. A shipload headed to Rapa Nui, but smallpox broke out en route and only 15 arrived at the island. They were put ashore. The resulting smallpox epidemic nearly wiped out the remaining population.
In the aftermath of the Peruvian slave deportations in the 1860s, Rapa Nui came under extensive outside influence from neighbouring Polynesian languages such as Tahitian. While the majority of the population that was taken to work as slaves in the Peruvian mines died of diseases and bad treatment in the 1860s, hundreds of other Islanders who left for Mangareva in the 1870s and 1880s to work as servants or labourers adopted the local form of Tahitian-Pidgin. Fischer argues that this pidgin became the basis for the modern Rapa Nui language when the surviving part of the Rapa Nui immigrants on Mangareva returned to their almost deserted home island.