Ideology is the proper concern of all historians of US foreign relations. Its relevance rests on one simple insight of fundamental importance. To move in a world of infinite complexity, individuals and societies need to reduce it to finite terms. Only then can they pretend an understanding of their environment and have the confidence to talk about it and the courage to act on it. All activities, whether individual or collective, require that simplifying clarity. Policymakers, or for that matter anyone confronting the world, get their keys to “reality” in the same ways that others in their culture do. A process of socialization begins in childhood and continues even as experience confirms or reshapes outlooks and influences behavior. Thus every foreign relations historian, like it or not, constantly comes in contact with the problem of ideology.

Of the many possible definitions, I favor one that identifies ideology as “an interrelated set of convictions or assumptions that reduces the complexities of a particular slice of reality to easily comprehensible terms and suggests appropriate ways of dealing with that reality.” Ideologies relevant to foreign affairs are in this sense sets of beliefs and values, sometimes only poorly and partially articulated, that make the world intelligible and interaction with it possible. This broad notion launches historians on a quest for ideas that give structure and meaning to the way policymakers and their people see the world and their country's place in it. This definition does not embody some ultimate truth. It is rather one plausible approach to understanding particular historical moments and personalities that deserves testing against other definitions of ideology.

Arriving at a definition is by itself an important step, which immediately alters the frame of reference. For those studying policymakers, the question becomes “not whether they have an ideology but to what ideology they subscribe; not whether ideology makes a difference but what kind of difference it makes for the shaping of their intentions, policies, and behavior.” But the question applies with no less force to the policy establishment, the media, public intellectuals, interest groups, and the public in general. The basic premise that ideology matters and that it is neither simple nor rigid suggests the importance of identifying fundamental notions (for example, about human nature, the constituents of power, and national mission) that policymakers and the public carry in their heads.