Karl Marx developed several influential theories about society and economics, including historical materialism, alienation, mode of production, class consciousness, and class struggle. Historical materialism views societal development and change as determined by material and economic conditions. Alienation refers to how workers lose control over their lives and destinies under capitalism. Marx saw class struggle and conflict between the bourgeoisie and proletariat as driving forces of historical change that could lead to a communist society without social classes. Marx's ideas had a major impact on social and political thought and some countries established communist systems based on his theories.