Djibo Hamani's L'Adar précolonial (République du Niger): contribution à l'étude de l'histoire des états Hausa is an interesting account of a region of the Hausa world sometimes forgotten or ignored. It's about what was really a peripheral area of the Hausa world, and one for which written sources only truly appear in the 1600s (although references to its powerful neighbors could be found a few centuries earlier). According to him, it was peopled by Azna (a Hausa population) that was once based in Air to the north, but migrated in small groups under different chiefly lineages by c. 1000 to 900 years ago, in various waves. they were probably migrating south due to pressure from Tuareg pastoralists and the declining environment of Air for agriculturalists. However, unlike the Gobir or Gobirawa Hausa, the Azna who migrated south into Adar never consolidated into a single state that ruled the area. It was then conquered by Kabi (sometimes spelled Kebbi, a Hausa state that was once part of the Songhay Empire under Askia Muhammad but then went its own way in the 1500s and became, for a time, a powerful Hausa kingdom dominating Adar and other Hausa areas. Then, after 1674, when prince Agabba of Agades defeated the ruler of Kebbi, the Agades Sultanate decided to annex Adar. Agabba, later deposed by his brother from the throne of Agades, moved south and established himself as the Sultan of Adar. Thus, Adar was unified under the Istambulawa sultanate of Air, which was, despite sometimes threatening other Hausa states or even Borno, was politically unstable (the Air sultan was seen by the Tuareg as a mediator and sometimes had little direct rule over the Kel Air Tuareg clans and tribes, which sometimes fought amongst themselves or defied directives from the Agades Sultan). So, long story short, the Adar Sultanate, a tributary of Agades, ruled a unified Adar but then later lost control of most of it in the 19th century.
The jihad of Uthman dan Fodio began in nearby Gobir, which caused changes in Adar since it too became, at least in theory, subject to the caliphs of Sokoto. The Adar ruling dynasty was initially split, like the Tuareg in Air, about supporting Uthman dan Fodio but once the sultan in Agades threw his support behind the jihad, Adar's ruling dynasty also accepted Sokoto. The caliph Muhammad Bello, son of Uthman dan Fodio, even gave the rights to the tribute of part of Adar to Tuareg allies. The 19th century then later saw the partition of Adar as the Kel Geres Tuareg took the Eastern part (they were more assimilated to the local area) while another Tuareg confederation seized the north of Adar. The Sarkin Adar, or local dynasty, was reduced to a small section of the province and lacked access to enough troops or revenue to seriously threaten or defeat the Tuareg who now dominated most of Adar. However, the 1800s saw the greater integration of Adar into the world of Hausa trade and international commerce and Islam spread more deeply. Adar's case is somewhat interesting as a peripheral Hausa region which never developed its own unified ruling dynasty until the Istambulawa of Air conquered it, but they themselves were reduced to little power in only a little more than a century. However, the 19th century witnessed more conversions to Islam, the growth of the mallam population, and, likely, an increase in the enslaved population as Adarawa and Tuareg traders traveled to Sokoto, Kano, and other markets.
Yet Adar's case makes one think that perhaps its Azna (local Hausa population of diverse origins) and their village-based level of political organization may have been what most of Hausaland was like before the development of the major states like Kano, Katsina, Gobir, etc. The close association between religious authority in the "animist" belief system and political authority in Adar may provide hints as to the origin of the earliest sarakauna in Hausaland. Furthermore, the case of Adar illustrates how loose the authority of Hausa or Central Sudanic states over other regions could be. Indeed, the Sultan of Agades, who could demand tribute from Adar, was clearly unable to assert his control over the region in any meaningful way in the 19th century to restore order. And despite Adar's importance for caravan routes to more important markets in Katsina and Kano, or even for the provision of horses to Kebbi (or Kabi) from Air, Adar remained rather peripheral in the grand scheme of Hausa states. Nonetheless, the region's larger significance in Hausa history can be found in a few episodes detailed by Djibo Hamani. For example, Jibril b. Umar, the mallam and scholar who had traveled to Egypt and Mecca and taught Uthman dan Fodio, was a native of Adar. Although his later jihadist movement differed from Jibril b. Umar on the question of Muslims who do not practice Islam lacking faith, Uthman dan Fodio clearly saw his teacher as the spiritual forerunner of his own attempts to restore and reform Islam in Hausaland. Later on, Adar also witnessed the rise of another reformer who imposed his own jihad in Adar, against the "animist" Azna and Tuareg who did not follow Islamic precepts. This figure, Muhammadu Jelani, was such a radical that he even preached social equality and racial equality in an Adar where the Tuareg nobility saw themselves as superior to the maraboutique clans as well as the Adar commoners.
Perhaps more recent scholarship can shed more light on the particularities of this region. Although based on both textual sources and oral traditions, Hamani's book was published in the 1970s. Today, with more advances in recent scholarship and perhaps new interpretations of the written sources, the history of Adar, and by extension, Kebbi, Air, and Gobir may challenge some of Hamani's conclusions. For instance, what exactly transpired between 1674, when Agabba of Agades defeated the ruler of Kebbi, and 1721 or so, when Agabba finally establishes himself permanently in Adar as the sultan. And perhaps the nature of Adar's role in trade between Air and Kebbi or Air and other Hausa states was more important than we realize, especially if the salines the Kel Air possessed access to before they gained control of Bilma's salt were already highly prized or valued. One also wonders about the relationship between the "pagan" cults of the Azna villages and the relationship with Islam after the Istambulawa conquest. If, for instance, the Kel Geres were already established in the eastern part of Adar and more sedentary, and even their nobles were more racially mixed than other Tuareg nobles, perhaps there was also a deeper penetration of Islam in the eastern part of Adar?