It’s not known yet which subregions of Upper Guinea contributed the most to Cape Verde’s genepool and in which approximate proportions. But based on historical/cultural/genetic clues I would rank them like this:
Guiné Bissau & Casamance (southern Senegal)
- The Mandinga empire of Kaabu and the Bijagos seem to have been the biggest slave suppliers. However slave raiding, factional fighting/civil wars and judicial enslavement were widespread among most Guinean ethnicities and especially the coastal ones.
- Cacheu already in the late 1500’s and later on Bissau emerged as the most important slave trading centers. Both of them located in Papel territory. Although they had extensive trading connections throughout Upper Guinea and also upriver with Kaabu, many of the slaves being sold were often from very nearby areas.
- The main conflicts resulting in large scale supply of captives appear to have been the wars between Cassangas and Banhuns in Casamance in the 1500’s/1600’s, the expansion of Kaabu into Tenda, Beafada & Banhun territory in the 1500’s/1700’s as well as the longstanding hostility between Mandinga and Fula in the late 1700’s & 1800’s.
Northern Senegal & Gambia
- The expansion and break up of the Wolof empire in between 1460-1549 provided the main source of slave trading for Cape Verde in this period. There’s a direct connection with the horse trade from Cape Verde. All Capeverdean travelling reports (Almada, Donelha, Lemos Coelho) from the 1500’s/1600’s mention this trade being principal and regret its loss in the late 1500’s.
- Gambia was considered among the best trading rivers by early Capeverdean writers. Especially the Cola (a fruit) trade from Sierra Leone into Gambia was deemed very important. Local warfare in between the splintered Mandinga states but also with the Banhun and Diola areas on the southern Gambia bank resulted in constant slave supply. There were also occasional wars with the Sereer state of Saloum (presentday Senegal), Fula and Kaabu. Besides that judicial enslavement (“chai”) seems to have been widespread.
- Most historians assume slave caravans from the deep interior (eastern Senegal/western Mali) only became dominant in the late 1600’s. However in early Portuguese sources various contacts with the inland empires of Mali and also Songhay and Fula have been mentioned.
Guiné Conakry & Sierra Leone
- Sierra Leone (in those days usually referring to northern Sierra Leone, a.k.a. Serra Leoa peninsula) would have been most important during the early period. Especially being dominant during the Mane invasions of 1550-1580’s when Sape slaves were probably most numerous among those imported from Upper Guinea. Guinea Conakry’s coastal area was inhabited by usually hostile Baga tribes. Still there was an important indigo trade. Except for the Cocoli area slave trade doesn’t seem to have been important at that time.
- Sierra Leone held a special place for Capeverdean settlers in the late 1500’s and early 1600’s. Its commercial potential was estimated to be bigger than that of Guiné Bissau. And there were several plans and heavy lobbying by Capeverdean elites to start a new colony in Sierra Leone, some proposals even suggesting transferring Cape Verde’s population to Sierra Leone! There was also an important Jesuit mission in the early 1600’s but it failed ultimately because of lacking support from Portugal and increased competition from especially the English.
- Starting from the 1730’s the Fula led Jihad from Fouta Jallon resulted into an increased supply of slaves. Ethnic solidarity was not guaranteed as both non-muslim Mande speakers (Malinke, Susu and Djallonke) as well as pagan Fula risked being enslaved. The main outlets of slave exports were situated along the Nunez and Pongo rivers which were never controlled exlusively by 1 European power until the late 1800’s.