In the 19th century, Karl Marx, his associate, and financial sponsor Friedrich Engels created the theory of a new political economy. According to this theory, a certain thing that is not produced for one's own consumption but in exchange for something else has a value it can be estimated in monetary terms. In Marx's theory, surplus value is the value created by the unpaid labor of a wage laborer. Surplus value, in Marxism, is the profit that the capitalist appropriates after all the costs associated with the production and sale of products. Consequently, the capitalists appropriate for themselves the fruits of the products produced by other people. The social injustice of the distribution of profits requires a change in this system and the construction of a just socialist society, where income will be distributed among all members of society, one way or another involved in the production of values.