Karl Marx's three-volume analysis of the capitalist mode of production, published from 1867 to 1894, which provided the theoretical foundation for socialist and communist movements worldwide. Capital argued that capitalism systematically exploits labour through the extraction of surplus value, that this exploitation is structural rather than incidental, and that capitalism contains internal contradictions that will produce its eventual crisis. The book's world effect ran primarily through the states and movements it founded rather than through academic economics.
Capital was not read by most of the people it transformed. Lenin read it. Mao read it. The founders of the Cuban Revolution read it. But the millions of workers who joined trade unions, the peasants who fought in revolutions, the leaders who built states in its name — most of them encountered Capital at second or third hand, through summaries, through party education programmes, through slogans derived from its arguments. This is how foundational texts actually work: not through mass readership but through the institutional structures that embody and transmit their core claims. Capital founded more states than any other secular text in history. Whether those states represented or betrayed its argument is the central question of twentieth-century political history.