The study of the historical, cultural, religious, linguistic, geographical and civilizational foundations of Oromo society is essential to understand the differences between the Oromo and Ethiopian peoples. The study of these differences is important in properly addressing historical contradictions which have emerged since the colonization of Oromia. First, we introduce Oromia and explain the process of its establishment. Second, we discuss the origin and branches of the Oromo and their modes of livelihoods, the gada system (Oromo democracy), world views, philosophy, and religion. Third, we explore the processes of class differentiation and kingdom formation in northern and western Oromia.