From these historical antagonisms and struggles arose the intellectual and political antagonisms, personified by the leaders of the social groups and classes, of which world-history relates: opposing religious and philosophical systems: Brahma and Buddha, Baal and Jahveh, National God and Universal God, Heathendom and Christendom, Catholicism and Protestantism, Materialism and Idealism, Realism and Nominalism. However abstract or metaphysical, however remote from actual life and material production they may appear to be, nevertheless, in the last resort they are to be traced back through many intermediate stages to changes in the economic foundation of the society in question, to the contradiction between this foundation and the conditions of production, as well as to the great struggles between conflicting interests which spring therefrom. The ethical, political, and politico-economic systems which strive with each other for mastery, as well as national and world wars, are separated from the real basis of society by a progressively smaller number of intermediate stages: the questions of idealist or utilitarian ethics, monarchy or republic, oligarchy or democracy, protection or free trade, State regulation or free scope for the economic forces, Socialism or private enterprise, etc., however lofty and humanitarian may be the arguments and ideal motives which their champions may adduce, are connected with the material foundation and the conditions of production which have come into conflict with it. Marx and Engels have set forth this conception in the Communist Manifesto, in popular form, as follows: "Does it require deep intuition to comprehend that man's ideas, views, and conceptions, in one word, man's consciousness, changes with every change in the conditions of his material existence, in his social relations and in his social life? "What else does the history of ideas prove than that intellectual production changes in character in proportion as material production is changed. The ruling ideas of each age have ever been the ideas of its ruling class. "When people speak of ideas that revolutionise society they do but express the fact that within the old society the elements of a new one have been created, and that the dissolution of the old ideas keeps even pace with the dissolution of the old conditions of existence. "When the ancient world was in its last throes the ancient religions were overcome by Christianity. When Christian ideas succumbed in the eighteenth century to rationalist ideas, feudal society fought its death-battle with the then revolutionary bourgeoisie. The ideas of religious liberty and freedom of conscience merely gave expression to the sway of free competition within the domain of knowledge."