Communism refers to a theoretical system of social organization and a political movement based on common ownership of the means of production. As a political movement, communism seeks to establish a classless society. A major force in world politics since the early 20th century, modern communism is generally associated with The Communist Manifesto of Karl Marx and Friedrich Engels, according to which the capitalist profit-based system of private ownership is replaced by a communist society in which the means of production are communally owned, such as through a gift economy. Often this process is said initiated by the revolutionary overthrow of the bourgeoisie (see Marxism), passes through a transitional period marked by the preparatory stage of socialism (see Leninism). Pure communism has never been implemented, it remains theoretical: communism is, in Marxist theory, the end-state, or the result of state-socialism. The word is now mainly understood to refer to the political, economic, and social theory of Marxist thinkers, or life under conditions of Communist party rule.