What came to be called the Cold War in the 1950s must be understood, to a large extent, as an ideological confrontation, and, whereas communism was manifestly an ideology, the “noncommunism,” or even the “anticommunism,” of the West was negatively ideological. To oppose one ideology was not necessarily to subscribe to another, although there was a strong body of opinion in the West that felt that the free world needed a coherent ideology if it was to successfully resist an opposing ideology.

The connection between international wars and ideology can be better expressed in terms of a difference of degree rather than of kind: some wars are more ideological than others, although there is no clear boundary between an ideological and nonideological war. An analogy with the religious wars of the past is evident, and there is indeed some historical continuity between the two types of war. The Christian Crusades against the Turks and the wars between Catholics and Protestants in early modern Europe have much in common with the ideological conflicts of the 20th century. Religious wars are often communal wars, as witness those between Hindus and Muslims in India, but an “ideological” element of a kind can be discovered in many religious wars, even those narrated in the Hebrew Bible (Old Testament), in which the people of Israel are described as fighting for the cause of righteousness—fighting, in other words, for a universal abstraction as distinct from a local and practical aim. In the past this “ideological” element has in the main been subsidiary. What is characteristic of the modern period is that the ideological element became increasingly dominant, first in the religious wars (and the related diplomacy) that followed the Reformation and then in the political wars and diplomacy of the 20th century.