claim to have produced a master key to history and that the materialist conception of history is not "an historico-philosophic theory of the , imposed by fate upon every people, whatever the historic circumstances in which it finds itself." In a letter to the editor of the Russian newspaper paper (1877), he explained that his ideas were based upon a concrete study of the actual conditions in Europe. Criticism of capitalism According to the Marxist theoretician and revolutionary socialist Vladimir Lenin, "the principal content of Marxism" was "Marx's economic doctrine." Marx demonstrated how the capitalist bourgeoisie and their economists were promoting what he saw as the lie that "the interests of the capitalist and of the worker are ... one and the same." He believed that they did this by purporting the concept that "the fastest possible growth of productive capital" was best for wealthy capitalists and workers because it provided them with employment. Exploitation is a matter of surplus labour—the amount of labour performed beyond what is received in goods. Exploitation has been a socioeconomic feature of every class society and is one of the principal features distinguishing the social classes. The power of one social class to control the means of production enables its exploitation of other classes. Under capitalism, the labour theory of value is the operative concern, whereby the value of a commodity equals the socially necessary labour time required to produce it. Under such conditions, surplus value—the difference between the value produced and the value received by a labourer—is synonymous with surplus labour, and capitalist exploitation is thus realised as deriving surplus value from the worker. In pre-capitalist economies, exploitation of the worker was achieved via physical coercion. Under the capitalist mode of production, workers do not own the means of production and must "voluntarily" enter into an exploitative work relationship with a capitalist to earn the necessities of life. The worker's entry into such employment is voluntary because they choose which capitalist to work for. However, the worker must work or starve. Thus exploitation is inevitable, and the voluntary nature of a worker participating in a capitalist society is illusory; it is production, not circulation, that causes exploitation. Marx emphasised that capitalism per se does not cheat the worker. Alienation (German: Entfremdung) is the estrangement of people from their humanity and a systematic result of capitalism. Under capitalism, the fruits of production belong to