the liberal historians or Marx, did not accord class struggle an integral role in social development. Within political economy, classes were determined by the 'natural' operation of the system of commercial exchange -- they simply followed from the natural inequality of property and the necessary effects of the division of labor. Some conflict between the classes might be seen as inevitable in the commercial system of capitalism, but these classes were certainly not defined by exploitation, and this 'class struggle' was not associated with historical development as such. For the historians, however, as Thierry most clearly demonstrated, it was precisely class struggle which was integral to development, because the aristocratic class had held back the bourgeois class. In this regard, Thierry closely followed Hume, freely associating aristocratic property with conquest. This historical element of struggle was entirely missing from political economy's conception of the development of property.
This thrust of liberal political ideology will be considered again in relation to the origins of Marx's thought. It should already be apparent that it was Marx who was uniquely responsible for bringing together ideas of political economy and economic development with the divergent liberal stream of the political history of class. What these two streams of thought had in common was the celebration both of 'commercial' or capitalist society and political liberalism, as the chief achievements of natural human progress. Marx would accept this as progress, but only as one side of the coin. In liberal political economy, specifically, he discerned an ideological rationalization of the other side, with which Rousseau had been concerned -- the social injustice that was created through the development of property.
This will be seen to have been the essential starting point of Marx's historical materialism. What Marx did not appreciate, however, was that though liberal political history differed substantially from political economy in its recognition of class struggle, it was no less integral an expression of liberal ideology. The incorporation of such liberal historical concepts as 'bourgeois revolution' into his work, though not calling into question Marx's historical materialism as such, has had a profound and regrettable effect upon Marxist analyses of pre-capitalist societies.