Social science research has denoted the role that exclusionary and divisive ideologies play in fortifying group boundaries and shaping inequality, including what is arguably its most extreme form—genocide. We know little, however, about where and why such ideologies emerge. This article analyzes 159 countries between 1955 and 2009 to assess the factors that influence the emergence and presence of exclusionary ideologies. Doing so informs broader social science conceptions of the role of culture and politics in the production of inequality and violence. I find that certain critical junctures, including independence and irregular regime change, are associated with the onset of exclusionary ideologies. Colonial histories and threats to political elites are also consequential. I conclude by discussing exclusionary ideologies relative to genocide as well as the general importance of cultural and political dynamics for future analyses of inequality.