Marx thereby refused the sharp separation of the economy and the state, and argued that the state embodied the interests of the capitalist class. This tradition of political economy survived in Marxist thought, although it was not greatly extended until the 1960s and 1970s, when it anchored a strong interdisciplinary approach that combined economic, sociological, and political perspectives in the analysis of capitalism—especially in the developing world. Dependency theory and world-systems theory are the most prominent among these.