One of the most basic concepts of Karl Marx's theory is the of "dialectical materialism". Marx thought of the dialectical nature of society and especially history is built on the tradition of G.W.F. Hegel which viewed history as a process of thesis, antithesis and synthesis, with each force in history creating an opposite one, driving society forward. But while Hegel was concerned with dialectical idealism, one of spirit, ideas and beliefs, Marx was more concerned with the material-economic side of social reality.
Marx developed his theory of dialectical materialism in the elaborate manner in "The Capital", but his views on the contradiction that propel society forward can be found already in his renown Communist Manifesto (and in The German Ideology). Marx bases the study of society on the study of inner contradictions. Contradictions within society are what, according to Marx the view of dialectical materialism, drive society forward. While Hegel thought the these contradictions are ideal, meaning that they are contradictions between different views and forms of thought, Marx held that they are in fact contradictions with material substance (hence "dialectical materialism").
According to Marx history can be described as an ongoing conflict between classes over the means of production. Nowadays, under the capitalist mode of production the main contradiction is between the needs of capitalists to profit and the needs of the worker to survive by retaining some of the profit. This conflict according to Marx originates from economic circumstances but is manifested in the realm of ideology, a product of the relations of production which serves to grant justification to the existing state. But under the approach of dialectical materialism, the class conflict will undoubtedly bring about change when the social structure can no longer sustain the burden. Dialectical materialism drives social change through the reciprocal relations between contradicting social factors, factors which have to do first and foremost with material considerations of economy and class, with ideology is a product of these considerations.