Modern historians have seen in the clash of interests, as the conjuncture of conditions and events favored one side or another, one of the universal factors in social and political change. In one of its broadest forms it appears in the conflict of older agrarian interests with the aggressive interests associated with commerce, finance and industry. In economic theory the concept of interests has not been so prominent. In earlier stages this was perhaps due to the identification of economics with “political economy.” The cameralists and the mercantilists took their stand on the solidarity of national economic interests. The historical dominance of interest groups has at various times been challenged by conceptions of society based on individualistic doctrines, such as those of the social contract and of natural rights. The physiocrats did work out a system of economics based on an assumption of the relative social utility of interest groups.