Party competition generally centers on a dominant dimension or dimensions of conflict that reflect the most salient political cleavages in a given society during a given period of time. The most common dimension of political conflict has traditionally been the left-right polarization of economic issues, which tends to reflect a class antagonism. In the late 1950s, Seymour M. Lipset summed up a huge body of findings that showed the correspondence between class interests and party support in established democracies. "The party struggle," he said, "is a conflict among classes, and the most impressive fact about party support is that in virtually every developed country the lower-income groups vote mainly for parties of the left, while the higher income groups vote mainly for parties of the right" (Lipset 1960:234).