The Fulani castes are endogamous in nature, meaning individuals marry only within their caste. This caste system, however, wasn't as elaborate in places like northern Nigeria, Eastern Niger or Cameroon. According to some estimates, by the late 19th century, slaves constituted about 50% of the population of the Fulɓe-ruled Adamawa Emirate, where they were referred to as "jeyaɓe" (singular "jeyado"). Though very high, these figures are representative of many other emirates of the Sokoto Caliphate, of which Adamawa formed a part. The castes-based social stratification among the Fula people was widespread and seen across the Sahel, such as Burkina Faso, Niger, Senegal, Guinea, Mali, Nigeria, Sudan, and others.