Although somewhat outdated, Nehemia Levtzion's Ancient Ghana and Mali remains the best introductory overview of 2 of the early major kingdoms of the Western Sudan. Gomez's African Dominion reflects more recent scholarship and advances in archaeology for the region, but suffers from a more hermetic nature, inaccessible style, and questionable attempts at integrating race and gender into the topic. Much of Gomez's text also degenerated into lengthy analysis on Songhay of interest only to specialists while neglecting some of arguments of other scholars. Levtzion's book, on the other hand, represents a fine, albeit dated, synthesis of oral traditions and textual analysis on the development of kingdoms, the spread of Islam, and trans-Saharan trade. Unfortunately, we just do not have enough sources on early Ghana or the early Malinke chiefdoms. In addition, perhaps inclusion of early Songhay history and the Kawkaw state would have been a good addition to encapsulate the entirety of the 3 "empires" of the Western Sudan from c.500 to c.1500.
While the scholarly consensus of today rejects the Almoravid "conquest" of Ghana, Levtzion's study demonstrates how the Western Sudan became increasingly incorporated into global medieval exchange and cultural development. The gold of the Western Sudan was pivotal for Mediterranean and European monetary systems and political transformations from the Italian trading centers to Fatimid expansion in North Africa. Trans-Saharan trade also reached the forest belt and coastal regions of West Africa as the gold fields of today's Ghana fed into the trading system of Mali. Local transformations with the spread of Muslim Dyula traders and Malinke warriors to the south and east, plus Islamic conversion of local rulers in more regions of Africa led to new developments, tastes, spiritual expression and trade between Western and Central Sudan. After all, the Wangarawa were in Hausaland by the 14th century and the Diwan of Kanem-Borno mentions Mali clerics coming to Kanem by the 13th century.
These early contacts between the Western and Central Sudan unfortunately do not appear in much of the external Arabic sources. An early trade route connecting Egypt and Ghana went through Kawkaw (Gao), and Tadmekka traded with Ghana and Kawkaw. Through Air and the early Hausa states, people from the Middle Niger and Kanem likely interacted as copper, salt, gold, textiles, and slaves were exchanged. Sadly, learning of what kinds of relations existed between Ghana or Mali and Kanem is difficult to uncover. Nonetheless, we would hazard, based on Levtzion's mention of intersecting trans-Saharan routes and the evidence of some cultural ties in other sources, that Kanem and the Central Sudan must have interacted through trade, religion and migration. After all, by the late 11th century, the ruling elites of Takrur, Ghana, Kawkaw (Gao), and Kanem were Muslims This convergence of Islamization in the most important kingdoms of the Sudanic belt in the Western and Central Sudan must have favored or fostered ties, diplomatic relations, and movements of Islamic clerics, as mentioned in the Diwan and Kano Chronicle. The two major "commodities" exported by the Western and Central Sudan, respectively, were gold and slaves. The lack of competition over the principal exports to North Africa and Egypt plus the development of textile industries in each region likely fueled exchange between the two zones.