Wikipedia
Gadaa (older spelling: Gada) is the traditional social stratification system of Oromos in Ethiopia and northern Kenya; it is also practiced by the Gedeo people of southern Ethiopia. Each class, or luba, consists of all of the sons of the men in another particular class. The entire class progresses through eleven different grades, each based on an eight-year cycle, and each with its own set of rights and responsibilities.
As of 1990, Gadaa had active adherents only among the Borana and Guji groups near the Ethiopian-Kenyan border. Though the Gadaa system itself is no longer widely practiced, it remains influential in Oromo society at large. Historically, it has been seen as a better method of governing than other forms in the region. However, the Gadaa had all the shortcoming and problems like that of the monarchial Oromo and monarchial non-Oromo Ethiopian systems of governance. In regions where the Oromo invaded and conquered, including around the Sidama and Somali, the Gadaa system was oppressive in practice, though proclaimed as democratic and just in Oromo oral tradition. According to ethnohistorian Ulrich Braukämper, minorities and those who assimilated, like the Hadiyya, were "considered to be of a lower social status than the 'pure' Oromo and did not possess equal rights in the Gadaa system."