Southern Ethiopia and the Christian Kingdom, 1508–1708: With Special Reference to the Galla Migrations and Their Consequences is Merid Wolde Aregay's seminal thesis on the Solomonic kingdom. Seeking to elucidate the fall of the centralized state and the decline of imperial control of a regimented military which had made the Solomonic state's expansion to the south possible, Aregay's state contextualizes this development with the history of Ahmad Gran's invasion, Oromo expansion, the Jesuits, and religious controversies between unctionists and tewahedo groups of the Ethiopian Church. Drawing on the voluminous royal chronicles, Jesuit sources, land charters, and travelogues, Aregay presents a convincing case for the various crises being so devastating to the Solomonic state due to the rise of the provincial nobility in power against the emperor.
Over time, imperial control was effectively lost in some provinces while the chewa regiments and professional soldiers either formed mutinous bands or became part of the provincial elite's retainers. Emperors like Lebna Dengel exacerbated these above problems through tyrannical rule and slave raiding that aroused opposition and even support for Ahmad Gran's conquest. The past ability of the Solomonic state to check the expansion of pastoralist lowland groups into the highlands was lost through the united Muslim front of Adal and the weakening of the military defenses and centralized imperial government. This only facilitated Oromo expansion as, in their early migration waves, Oromo clans were often more effective as there was enough land and booty for various clans to collaborate in their raids. The military, through its ineffectiveness or imperial abandonment of provinces, led to some peasants and tributaries bearing arms to defend themselves or becoming dependents or clients of Oromo groups.
Subsequent emperors, particularly after Galadewos, continued the trend of weakening central authority and the military by relying on slave raiding, not resisting the growing autonomy of regional governors and nobility, and failing to check rapid Oromo expansion. Minas, who was a pawn of his mother and her influence, and Sarsa Dengel who succeeded him, were often ineffective or unable to check provincial officials like the bahr negash Yeshaq. Later neguses, such as Susenyos, a former bandit, tried to administer the empire by allowing the provinces to be mostly ruled by his brothers and sons-in-law. Susenyos, according to Aregay, weakened the position of emperor by rejecting the pomp and ritual associated with his office. His reliance on slave raids targeted non-rebellious pagan Agaw and other groups to raise revenue instead of reforming the administrative structure of the empire to increase revenue derived from the provinces. The attempt to impose Catholicism on the population drove the Church into revolt, further weakening the central government as it illustrated for posterity that the Church could act independently of the emperor.
This contributed to the later conflicts within Ethiopian Christianity between the unctionists and orthodox positions on Christological controversies. Unfortunately, these religious controversies became even more problematic in the 17th and 18th centuries as emperors from Fasiladas to Iyasu I struggled to contain the conflicts between clerical and monastic groups that involved nobles, warlords, and Oromo groups in their struggles with each other and the imperial court. Thus, even a "traditionalist" emperor like Fasiladas appeared to rule a state with flimsy foundations as the Solomonic state faced internal Christian religious division, Oromo raiding, nobility vs. imperial court intrigues or civil wars, and pretenders to the throne. In other words, the system which had been established by the early Solomonic rulers that had led to the formation of an empire was not maintained.
For the interests of this blog, it is interesting how the Solomonic Dynasty appears to have followed a similar trajectory to the Sayfawa during this same period. The Sayfawa appear to have reasserted themselves in the Central Sudan as a major power from c.1500 until the early 18th century. While Sayfawa rule seems to have declined after Ali b. Umar in the 17th century, Sayfawa rule may have suffered from overtaxation of the peasantry, slave raiding on certain tributary or predatory areas that could have been more effectively integrated into the core, and the increase of mallamtis and Sufi centers that might have challenged the imperial court's authority or religiously-based legitimacy. Some of the seeds of their decline may have already been evident in the uprisings, political discord and factions over succession, and inability to protect the western frontier from Tuareg bandits, lacustrine settlements from Yedina attacks and Kanem and Kawar from Tubu and Tuareg incursions. However, like their Solomonic counterparts, the Sayfawa occasionally produced great or competent mai who attempted to challenge the decay or complacency of the court. But circumstances eventually reached the point where the mais were unable to stamp resistance from former tributaries like Mandara.