 When he suspected the Portuguese of receiving illegally enslaved persons to sell, he wrote letters to the King João III of Portugal in 1526 imploring him to put a stop to the practice.The kings of Dahomey sold their war captives into transatlantic slavery, who otherwise may have been killed in a ceremony known as the Annual Customs.As one of West Africa's principal slave states, Dahomey became extremely unpopular with neighbouring peoples.