The thesis that, in the advanced capitalist societies, class conflict has been institutionalized; that is, has become controlled, and has therefore declined. This is said to result from the separation of political and industrial conflict (so that disputes in one sphere no longer reinforce lines of schism in the other) and by the extension of citizenship rights and greater equality of opportunity. Liberal political theorists often advanced this argument during the 1950s and 1960s. A good sociological example is Ralf Dahrendorf 's Conflict after Class (1967). See also incorporation.