Peoples and nations are attempting the most basic question humans can face: Who are we? And they are answering that question in the traditional way human beings have answered it, by reference to the things that mean most to them. People define themselves in terms of ancestry, religion, language, history, values, customs, and institutions. They identify with cultural ethnic groups: tribes, ethnic groups, religious communities, nations, and, at the broadest level, civilizations. People use politics not just to advance their interests but also to define their identity. We know who we are only when we know who we are not and often only when we know whom we are against.
Samuel P. Huntington: The Clash of Civilizations and the Remaking of World Order