This paper highlights the fact that language endangerment in some multilingual developing societies is causal to the violent ethnic conflicts in those societies. Endangered language identity groups shift to the dominant language groups. But, over time, a concatenation of factors and nuanced realisation of perceived marginalisation (showing overtly at the political, economic, social and religious realms) leads to attrition in the wake of the endangered groups' clamour for fair treatment. The cases of Benue, Plateau and Taraba States in Middle Belt Nigeria (involving the Tiv, Jukun, Etulo, Kuteb, Berom, Afizere, Anaguta, Taroh, and Hausa ethnic groups) reveal this fact. Highly significant calculated "t"-test values at an alpha level of less than 0.05 are found, for example, to show the disintegration of bilingual behaviour between Tiv/Jukun and Tiv/Etulo during the period of the violent ethnic clashes among them. Language endangerment/shift reversal is complex. It can create conflicts but at the same time help to restore confidence and mitigate the fear of domination felt by ethnic minorities. Linguists and small/dominated language communities can work assiduously towards the latter. Conflict management experts will also do well to pay a great deal of attention to language as a conflict agent. (Contains 8 tables and 5 notes.)