The Comoros Genocide

Comoros is a small island country with 851,000 people between Madagascar and the continent of Africa which shares a largely common history with Madagascar up through its first encounter with Portuguese explorers in 1503, and was a trading post for Indian Ocean Arabian seafarers after early contact with Austronesian sea farers from Southeast Asia ceased.

The historical population of Comoros, however, was almost complete replaced in the time period from 1790 to 1820 in a little know historical African genocide:

In the last decade of the 18th century, Malagasy warriors, mostly Betsimisaraka and Sakalava, started raiding the Comoros for slaves and the islands were devastated as crops were destroyed and the people were slaughtered, taken into captivity or fled to the African mainland: it is said that by the time the raids finally ended in the second decade of the 19th century only one man remained on Mwali. The islands were repopulated by slaves from the mainland, who were traded to the French in Mayotte and the Mascarenes. On the Comoros, it was estimated in 1865 that as much as 40% of the population consisted of slaves.

France first established colonial rule in the Comoros by taking possession of Mayotte in 1841 when the Sakalava usurper sultan Andriantsoly [fr] (also known as Tsy Levalo) signed the Treaty of April 1841, which ceded the island to the French authorities.