Multilevel structural analysis links the macrostructures of large populations in successive steps to the network structures in face-to-face groups. Macrostructure is conceptualized as a multidimensional space of positions among which people are distributed. Three generic dimensions of social structure are heterogeneity, inequality, and intersecting social differences (in various respects). All three promote intergroup relations. Any one of them can be decomposed into the part resulting from its equivalent differences within and that resulting from those among substructures. The further any differentiation penetrates into substructures, the more probable are intergroup relations.