Le développement et la régression chez les peuples de la boucle du Niger à l'époque précolonial by Michael Tymowski is an ambitious work. An attempt to make sense of around 1000 years of economic progress and regression along a key part of the Western Sudan (centered on the Middle Niger), Tymowski relies heavily on the Timbuktu chronicles, external Arabic sources, and oral traditions. He persuasively makes the case for economic development with the growth of urban centers, limited private land tenure, and accelerated long-distance trade, which later declined in the 1600s and 1700s. This shows that the history of "development" in sub-Saharan African areas has always been dynamic, and not simply one of timeless "backwardness" or irrelevance.
However, Tymowski's study is quite outdated and relies on French translations of sources in Arabic. It also relies heavily on Jean Rouch and other somewhat outdated scholarship on Songhay ethnography and oral traditions, even repeating the unproven claim that the Dia/Za dynasty of early Songhay rulers were actually Lemta Berbers. In addition, he heavily relied on the problematic Tarikh al-Fattash chronicle for assertions about servile/caste populations. This dependence on French translations of Arabic sources and outmoded scholarship on Songhay ethnography and oral traditions suggest possible limitations of Tymowski's study. While one must acknowledge that the aforementioned Timbuktu chronicles are probably reliable for the 1400s and 1500s (at least more so than for earlier centuries), Tymowski's attempt to derive meaningful conclusions or theories about the economic development of the Mali Empire and Songhay Empire may be misleading or problematic. Nonetheless, there are a number of intriguing ideas about the relationship between the towns (Gao, Djenne, Timbuktu) and the countryside, as well as the role of the state in promoting land tenure arrangements along the lines of property property or through state domains (those of the askias) that controlled and promoted the redistribution of goods.