The theory of class structure is at the center of Karl Marx's social theory, for it is the social classes formed within a particular mode of production that tend to establish a particular form of state, animate political conflicts, and bring about major changes in the structure of society. Class structure consists of the different economic levels in a society, and the opportunity for upward mobility (or lack thereof). It usually consists of an Upper, Middle, and Lower class, and various subclasses. Marxist class theory denies the imperative that all men are created equal.