The Situationist International (SI) was an international organization of social revolutionaries made up of avant-garde artists, intellectuals, and political theorists. It was prominent in Europe from its formation in 1957 to its dissolution in 1972. The intellectual foundations of the Situationist International were derived primarily from libertarian Marxism and the avant-garde art movements of the early 20th century, particularly Dada and Surrealism. Overall, situationist theory represented an attempt to synthesize this diverse field of theoretical disciplines into a modern and comprehensive critique of mid-20th century advanced capitalism. Essential to situationist theory was the concept of the spectacle, a unified critique of advanced capitalism of which a primary concern was the progressively increasing tendency towards the expression and mediation of social relations through images. The situationists believed that the shift from individual expression through directly lived experiences, or the first-hand fulfillment of authentic desires, to individual expression by proxy through the exchange or consumption of commodities, or passive second-hand alienation, inflicted significant and far-reaching damage to the quality of human life for both individuals and society. Another important concept of situationist theory was the primary means of counteracting the spectacle; the construction of situations, moments of life deliberately constructed for the purpose of reawakening and pursuing authentic desires, experiencing the feeling of life and adventure, and the liberation of everyday life. The situationists recognized that capitalism had changed since Karl Marx's formative writings, but maintained that his analysis of the capitalist mode of production remained fundamentally correct; they rearticulated and expanded upon several classical Marxist concepts, such as his theory of alienation.