A prominent literature shows the benefits of awarding political and cultural rights to ethnic minorities. However, minority accommodation often sparks backlashes from the ethnic majority. The anti-minority violence perpetrated by India's Hindutva movement and Rwanda's former Hutu Power movement are only the most drastic examples. Yet, in light of its documented pacifying effects and material benefits, widespread resistance against even symbolic accommodation is puzzling. In this article, I address this puzzle, focusing on majority grievances and threat perceptions. As regards institutional form, I argue that majority backlashes are more likely where minority accommodation is based on explicitly ethnic criteria. Thereby, it visibly deviates from norms of majority rule and activates injustice frames. As regards societal context, I argue that majority backlashes are more likely where accommodation targets minorities with a history of civil conflict and where it is implemented during phases of regime transition. Under such circumstances, it risks sparking especially pronounced perceptions of threat. To test these arguments, I introduce new monthly data on proposed and implemented minority accommodation, majority affirmation in state constitutions, and ethno-cultural majority mobilization. I use these data to conduct a quantitative analysis covering all multi-ethnic states since the end of the Cold War. I complement this with process tracing in several purposefully-chosen typical cases. My findings highlight the difficult trade-offs facing policy-makers in divided states, who may be caught between opposing demands of ethnic majority and minorities. Moreover, they underline the importance of incorporating majority nationalist mobilization into conflict research more broadly.