Marxism, or dialectical and historical materialism, has served as both the explanatory theory of history and social development and the theoretical basis for socialist and communist movements in the later nineteenth and twentieth centuries. What is the role of stages of history, of material conditions and consciousness, to Marxism as a theory of history? What is the role of dialectical relationships, forces of production, and relations of production, to Marxism as a theory of history and social development? What is the role of class struggle and revolution to Marxism as a theory of history and social development? What, according to Marxism, are the unique features of capitalism as a system and why, in Marxist theory, must capitalism be replaced by socialism for civilization to advance?