Caste systems in Africa are a form of social stratification found in numerous ethnic groups, found in over fifteen countries, particularly in the Sahel, West Africa, and North Africa. These caste systems feature endogamy, hierarchical status, inherited occupation, membership by birth, pollution concepts and restraints on commensality. The specifics of the caste systems in Africa vary among the ethnic groups. Some societies have a rigid and strict caste system with embedded slavery, whereas others are more diffuse and complex. Countries in Africa that have societies with caste systems include Mali, Mauritania, Senegal, Gambia, Guinea, Ivory Coast, Niger, Burkina Faso, Cameroon, Liberia, Sudan, Sierra Leone, Algeria, Nigeria, Chad, Ethiopia, Somalia, Djibouti, Eritrea and others. While it is unclear when and how the caste systems developed in Africa, they are not ancient and likely developed sometime between the 9th century and 15th century in various ethnic groups. East Africa There has been much recent scholarship on caste systems in the Horn of Africa. They have been studied in communities that speak Semitic, Cushitic, and Omotic languages. The term "Manja" or ""Manjo" is found repeatedly.<ref>Hailu, Gebreslassie Kiros. "Social Stratification and Marginalization in the Southern Nations Nationalities and People Region of Ethiopia: The Case of Manja Minority Groups." Global Journal of Human Social Science: C Sociology & Culture 16, no. 6 (2016): 52-58.</ref> The terminology used by various scholars has varied but they have found consistently found links between social groupings and occupations, often potters, metal workers, weavers, leather workers. This list of sources is incomplete, but contains important sources. Amhara people The social stratification of the Amhara people of Ethiopia includes castes. According to Donald Levine – a professor of Sociology specializing in Ethiopian society, the Amhara society has consisted of high-ranking clans, low-ranking clans, caste groups (artisans), and slaves. The Amhara caste system was hierarchically higher than its lowest slaves strata. The Amhara caste system consisted of: (1) endogamy, (2) hierarchical status, (3) restraints on commensality, (4) pollution concepts, (5) each caste has had a traditional occupation, and (6) inherited caste membership. This caste system has been a rigid, endogamous and occupationally closed social stratification among Amhara and other Afro-Asiatic-speaking Ethiopian ethnic groups. However, some state it as an economically closed, endogamous class system or as occupational minorities, whereas others such as the historian David Todd state that this system can be unequivocally labelled as caste-based. Borana people The Borana people are