Ethiopia is a multicultural and multilingual country. The Oromo and Somali communities are found in the same linguistic community, that is, the Cushitic language. Historically, Somalis and Oromo have a long tradition of co-existence and strong socio-cultural interactions, as well as antagonistic relationships and intermittent conflicts. Traditionally, the major sources of conflict between the two communities were competition over scarce resources, territorial expansion, livestock raids and counter raids, kidnapping for marriage purposes and the revenge tradition. However, this time the conflict took a different nature, form and bigger scale causing devastation never seen in the history of communal conflict in the country. The study has utilised primary and secondary data collection and employed narration and content analysis to realise the objective of the paper. The findings of this study reveal that the causes of the Oromo–Somali conflict are complex and dynamic. This urges the need to carry out a deeper investigation beyond the federal arrangement. Thus, fundamental and triggering factors including the involvement of internal and external forces, the collapse of social norms and prevalence of moral anarchism, socio-economic issues, competing interests among public and military officials, poor leadership and governance system, competing interests over resources, aspects of local cultural institutions in regulating inter-ethnic relationships are identified in fuelling ethnic conflict in the studied area. Since the conflict in the region is much more complex than the dominant narrative of resource scarcity and ethnic politicisation, open democratic dialogue, genuine consultation and negotiation at a different level with various interest groups, stakeholders and community representatives, militant groups operating in the area is of paramount importance to ease the increasing ethnic tension and political crisis in order to build sustainable peace in the region.