Saint-Domingue was the French colony on the western third of Hispaniola and, by the late eighteenth century, the most profitable plantation colony in the world. Its population was overwhelmingly enslaved, overwhelmingly African-born because mortality was so high that the workforce was replaced by importation rather than reproduced, and drawn from a range of West and Central African peoples.
What became Haitian Vodou was assembled in those conditions. People arriving from the Bight of Benin brought the vodun of the Fon and Ewe, people from the Kongo brought a different system, Yoruba practice arrived with others, and none of them arrived with their shrines, their lineages or their ritual specialists intact. Baptism was legally required and Catholic instruction minimal, which supplied a further vocabulary of saints, prayers and images. The result is a tradition with distinct rites within it, Rada and Petwo above all, whose differences preserve those origins rather than blurring them.
Its structure is recognisably African: a distant creator, a working population of spirits called lwa who are served with drumming, song, food and dance and who arrive by possessing devotees, and the dead as continuing participants. Its calendar and its imagery are partly Catholic. It is not a syncretism in the sense of a blend that lost its parts; the parts remain identifiable, and practitioners distinguish them.