Marxism, social and political theory based on the works of Karl Marx and his followers, associated with the socialist and communist movements. Marx's works can be broadly divided into his early philosophical writings (for example, the posthumously published �konomisch-philosophische Manuskripte aus dem Jahre 1844/Philosophic and Economic Manuscripts of 1844, Die deutsche Ideologie/The German Ideology, 1845-1846), his pamphlets (for example, Manifest der kommunistischen Partei/The Communist Manifesto, 1848), his analyses of contemporary events (for example, Der Achtzehnte Brumaire des Louis Napoleon/The Eighteenth of Brumaire of Louis Napoleon, 1852, and Der B�rgerkrieg in Frankreich/The Civil War in France, 1871), and his mature and fundamental works, Zur Kritik der politischen �konomie (Contribution to the Critique of Political Economy, 1859), and, above all, Das Kapital (vol. 1, 1867; vols. 2 and 3 published posthumously). To summarize, let alone explain, this vast and complex theoretical system in a few paragraphs is impossible. The ramification of the doctrine have included philosophy, economics, history, politics, and most of the social sciences. No theorist has been as analysed and discussed in the 20th century as Karl Marx. The reason behind this attention is far from being purely academic. No comparable modern thinker has had as much impact on political parties and movements. Prior to the collapse of communism in Europe one-third of humanity was under regimes purportedly inspired by Marx's works.

Marx sought to unveil the inner laws of the development of capitalism. Each historical epoch was said to be characterized by a specific mode of production to which corresponds a particular system of power and, consequently, a ruling class in constant open or hidden conflict with an oppressed class. Thus feudal society is dominated by a feudal mode of production in which the class of landlords extracts a surplus from a rural population bound to the land. Transitions from slavery to feudalism and from feudalism to capitalism occurred when the forces of production (that is, labour power and the actual means of production such as machines) could no longer develop within existing relations of production, that is the relations between classes. For example, the crisis which overcame feudalism when capitalism's need for a growing working class required the elimination of traditional legal and ideological arrangements which tied serfs to the soil.

In capitalism the fundamental relation, the wage relation, is based on a contract between juridically equal parties. The owners of capital (capitalists) pay the workers (the proletariat) wages in return for an agreed number of working hours. This disguises a real inequality: the capitalists "cheat" the workers by appropriating far more than they pay out in wages and other necessary production costs. This special and statistically unquantifiable appropriation, or "surplus value", gives the owners of capital great wealth and control over the economic development of society. They thus appropriate not simply wealth but also power. A complex political superstructure, consisting of laws and ideologies of various types, regulates and reinforces these social relations. In effect, by being in charge of the surplus which results from accumulation, capitalists can determine the overall direction of society. The commodities produced by capitalism must possess "use-value", otherwise they would not find buyers, but to the capitalist they must have exchange-value: they are not needed for the capitalist's own consumption but only to be exchanged for money. Thus capitalist production is essentially production for exchange and not for needs. Competition drives inefficient capitalists into bankruptcy and leads to concentration and monopolies. Markets, however, are constantly expanded while techniques of production and forms of exchange are ceaselessly revolutionized.

Crises are central to capitalism. Capitalists are driven to try to increase the length of the working day, its intensity, or the productivity of labour. Workers, if appropriately organized, will offer resistance. Capitalists try to enlarge their markets while paying their workers as little as possible. Yet if they all succeeded, workers' consumption and so their demand would decrease, markets would shrink, and capitalism enter into crisis. Marx's complex and at times obscure writings allowed for disparate interpretations. Before 1914 the dominant orthodoxy was that propounded by Karl Kautsky, who stressed the inevitability of capitalism's collapse. After the Russian Revolution, Vladimir Illich Lenin added to the Marxist canon a theory of imperialism, a theory of the state, and principles of revolutionary organization�hence Marxism-Leninism. The Italian communist Antonio Gramsci stressed the role of ideology in civil society in the construction of political hegemony. The appeal of Marxism was that it gave powerful intellectual backing to the moral outrage arising from the purported iniquities of capitalism and to the hope that a system which ought to disintegrate would eventually do so. The theory was sophisticated enough to appeal to the intellectually minded while being amenable to simplification and diffusion at a mass level by socialist activists. Since 1945 most socialist parties have renounced Marxism, while the study and development of the doctrine has remained largely confined to academic circles.