This article uses the resource scarcity-violence model of Homer-Dixon (1999) to analyse the drivers of conflicts between ethnic groups that shared the pre-colonial ethnic frontiers of trans-Jubaland–Wajir and competed over water sources during the colonial period in the Northern Frontier District (NFD) of Kenya from 1903 to 1939. The article shows that pre-colonial ethnic conflicts were not induced by resource scarcity. Rather, extended periods of peace punctuated by conflicts were associated more with social and political relations. By contrast, the colonial period, with far more restrictive resource access to wells and the grazing lands, resulted in structural changes in resource scarcity. Colonial resource governance was incapable of stopping the pressures from migrants threatening resident populations. Residents were finally displaced and former alliances broken up. The competition resulted in violent conflicts due to structural changes that altered rights to resources.