Paul Lovejoy's Salt of the Desert Sun: A History of Salt Production and Trade in the Central Sudan is required reading for anyone interested in the production and trade of one of the major commodities used in the "Central Sudan" region of West Africa. Although mostly based on 19th century and colonial-era sources on salt production, markets, social relations, and political economy, Lovejoy's important study elucidates the importance of salts in the regional economy. If one can stomach the somewhat duller early chapters, the second half of the book contains rich details and references for specifics on social relations, labor, proprietorship, political factors, and changes in the development of salt production. While technologically quite "primitive" and limited by climactic variables and transportation, the role of salt in the region's economy was significant. It even contributed to Hausa and Central Sudan trade with the Volta Basin, especially for kola nuts. Indeed, the full scale of it can only be glimpsed because of our limited sources which largely date from the 19th and 20th centuries.
So, how did the Central Sudan's salt trade impact the development of Borno and Borno's hegemony in the region? For much of the precolonial era, particularly before the c.1759, Borno was the closest to creating a quasi-monopoly of salts in the region. Due to Borno's control of the Kawar desert salines as well as Sahelian and Lake Chad sources (salt and natron), it became the dominant player in the salt trade for centuries, probably as early as the 16th century. Salt was used for livestock, medicinal purposes, culinary tastes and industrial uses (tanning), so it was directly linked to agriculture, textiles, leatherwork, and long-distance trade. By controlling most of the sources of salts in the region before the Tuareg affiliated with Agadez seized control of the trade of Bilma by 1759, Borno was in a tremendous position to dominate the larger economy of the area. Borno's salt works in Mangari, or Gourbei, for instance, were relatively close to the capital city and its populous district. This district, according to Lovejoy, was also an agricultural center with a local textile industry. Lake Chad also served as a center for livestock-raising, which profited Borno's economy as it still dominated Kanem on the eastern shores of Lake Chad.
Although the control of Kawar was central to Borno's interests in trans-Saharan trade, Lovejoy's text convincingly illustrates how the desert salines of Bilma and Fachi contributed to the bustling trade in salt across the Central Sudan. Additional sources of salt in the Sahelian region of Borno also contributed to the strong regional economy, which surely contributed to Borno's preeminence as the predominant power in the region. As Barkindo argued in the UNESCO series, Borno in the 1500s-1700s possessed a strong regional economy and salt surely played a role. Despite the limited sources, Lovejoy speculates that control of salines in the semi-arid Sahel zone of Borno was likely distributed through fiefs, whose holders were mostly based in Birni Gazargamo. Fief-holders and others who jostled for lucrative grants of fiefs may have relied on slave labor in Gourbei and other regions, suggesting that slaves procured via raids and trade with Bagirmi could have found local uses in Borno's local industries. Consequently, one can see how trans-Saharan and regional trade supported each other through various linkages.
Unfortunately, this strong regional economy began to decay by the 18th century. The main victor of this process was the Sokoto Caliphate and the Hausa traders (though many were actually of Kanuri and Tuareg origins). The Tuareg of Agadez were able to seize control of the distribution of salt from Bilma and Fachi while continuing to supply salt from Teguidda to Hausaland. Increasingly, after 1759, the trade routes reoriented through the Tuareg networks in the desert to Hausa cities like Kano. Hausa traders, who were active in the kola trade, textile manufacturing and exports, and, through Kanuri-descended "Beriberi" traders, had access to salts from Borno and Foli in Kanem, were able to become the dominant market for salts while supplanting Borno's role. As convincingly laid out by Lovejoy, Borno gradually became an economic satellite of the Sokoto Caliphate, despite still occupying some importance from its Sahelian and Lake Chad salines. One would think the rise of Hausa traders moving kola nuts into the Central Sudan, plus the increase in textile production in areas such as Kano further eroded what remained of Borno's textiles and trade network.
Thus, the Tuareg, by defeating the Koyam and nomadic allies of the Sayfawa rulers in the 18th century, replaced the Kanuri in the movement of desert salts to the savanna lands further south. Hausa traders and networks gradually replaced Borno merchants while incorporating some into their networks. Borno gradually became dependent on the Sokoto Caliphate after losing western territories, the Kawar, and, eventually, Kanem. Despite only being one of the major commodities exchanged in the Central Sudan, the loss of dominance of the salt trade was undeniably linked to Borno's gradual decline in the 18th and 19th centuries. Exactly how and why Borno's nomadic allies were defeated by the Tuareg and the Sayfawa rulers did not make more consistently forceful attempts to reassert their authority in Kawar is not clear. Regardless, their lack of forceful action in the late 18th century probably contributed to the weakness of the Sayfawa rulers in the face of Fulani jihadist attacks in the early 19th century. The Great Drought of 1738-1753, the defeat of Borno by Mandara in 1781, and possibly another drought in the 1790s or early 1800s must have also played a role in the long decline of the Sayfawa rulers.