Religious suffering is, at one and the same time, the expression of real suffering and a protest against real suffering. Religion is the sigh of the oppressed creature, the heart of a heartless world, and the soul of soulless conditions. It is the opium of the people.
History is not like some individual person, which uses men to achieve its ends. History is nothing but the actions of men in pursuit of their ends.
The history of all hitherto existing society is the history of class struggles.
The theory of Communism may be summed up in the single sentence: Abolition of private property.
The proletarians have nothing to lose but their chains. They have a world to win.