Federal states in which component regions are invested with distinct ethnic content are more likely to collapse when they contain a core ethnic region, a single ethnic region enjoying pronounced superiority in population. Dividing a dominant group into multiple federal regions reduces these dangers. A study of world cases finds that all ethnofederal states that have collapsed have possessed core ethnic regions. Thus, ethnofederalism, so long as it is instituted without a core ethnic region, may represent a viable way of avoiding the most deadly forms of conflict while maintaining state unity in ethnically divided countries.