Throughout this report the committee recognizes that the targets of potential attack—transportation, communication, and energy systems, for example—are systemically related, and that an attack on one spreads to and perhaps cripples others. This principle of “systemness” applies to the organization of human life as well. It has been recognized for more than two centuries—notably in the work of Adam Smith (1937 (1776)), Herbert Spencer (1897), and Émile Durkheim (1949 (1891))—that as commercial, technological, and industrial development proceeds, social activities become progressively more differentiated and at the same time more mutually dependent. This is readily recognizable in the case of economic specialization, wherein the sites of production (firms, service agencies) come to be organized separately from the sites of consumption (households and organizations). This principle applies to other institutional spheres as well. In premodern times the family assumed responsibility for educational, medical, and welfare functions that have since become structurally separated and now reside in schools, hospitals, and government agencies.
Differentiation and mutual dependency constitute sources of vulnerability. The crippling of an industry responsible for vital products (such as food) or of the financial, medical, or legal system can injure (through deprivation) all those who are dependent on it and cannot readily perform its activities themselves. The effects can be even more serious if the damage is widespread, when repairing, rebuilding, or replacing lost functions may become long-term matters.
The growth of a complex industrial and service-based society not only leads to differentiation of social roles and of the institutions that directly affect individuals, but it also makes for a more complex group life. A panoply of groups based on economic interest—such as business groups, professional associations, and labor unions—sometimes cooperate with other groups and sometimes come into conflict with them. Modernized societies also evolve a system of social classes that crosscut associational life. Historically, the class dimension has not been a prominent feature of American society (as it was in many European societies), but during periods of labor disturbance such as the Great Depression, class interests have become more salient. Finally, the United States is characterized by many groups based on religious, ethnic, and racial identity, deriving historically from the heritage of slavery and waves of immigration that continue up to the present. These groups constitute bases for community association as well as social and political identity. Historically, relations among them have been variable as well, encompassing friendliness, accommodation, competition, latent tension, and, occasionally, open conflict and violence.