Marx thought that the way a society was organized was determined by economic factors, i.e., division of labor and control of the means of economic production. Class conflict was a recurring fact in Marx's philosophy, and it originated when changes in the economic base occurred that changed the relationship of social classes to the means of production. The advent of capitalism had led to the bifurcation of social classes into what Marx called the proletariat and the bourgeoisie. The proletariat were those who were alienated from control of the means of production, and they had to sell their labor as a commodity in order to survive. The bourgeoisie, on the other hand, had supplanted the landed feudal nobility as the class that controlled the means of production. As Marx and his colleague Frederich Engles described it in their Communist Manifesto:
The modern bourgeois society that has sprouted from the ruins of feudal society has not done away with class antagonisms. It has but established new classes, new conditions of oppression, new forms of struggle in place of the old ones. Our epoch, the epoch of the bourgeoisie, possesses, however, this distinctive feature: it has simplified the class antagonisms. Society as a whole is more and more splitting up into two great hostile camps, into two great classes, directly facing each other: Bourgeoisie and Proletariat.
But Marx also argued that the very logic of capitalism would lead to the destruction of the bourgeoisie. The brutal competition that characterized capitalism meant that the bourgeoisie had to introduce new technology, techniques, and modes of social relations that would not only alienate workers even more from the value of what they produced, but would drive more and more middle class people into the ranks of the proletariat. Much of Das Kapital was spent illustrating exactly how Marx thought that would happen. Eventually, Marx thought, the proletariat would become so large, and so alienated and impoverished, that it would rise up to destroy the bourgeoisie and seize control of the means of production. The result, he suggested, would be communism, a classless society. This is an extreme oversimplification of Marx's understanding of class, which has been very influential in Western thought. But the essential thing is that Marx perceived capitalism to have ushered in the bourgeoisie and a new, revolutionary class, the proletariat.