Does ethnic structure affect the occurrence of civil conflict and, if so, how? This study develops an agent-based model of endogenous grievances that builds on the new constructivist conceptualization of ethnicity and the theories of group inequality and crosscuttingness. Specifically, I simulate conflict as a function of spontaneous economic disparities between nominal "ethnic groups" with no predefined salient categories and related antagonism. Then I apply the model to reconsider the effect of (bidimensional) ethnic structure on conflict, which has been largely dismissed in recent scholarship. By varying the parameters of ethnic demography in artificial societies, I conduct a series of replicable experiments revealing that various structural settings yield systematically different patterns of conflict. While there is no "most hazardous" structure per se, both polarization and crosscuttingness appear to decrease the likelihood of violence but increase its potential deadliness, which indicates a more general tradeoff of conflict incidence and intensity.