“Realism” is probably the second oldest perspective we have on the place of ethics in international politics. The oldest, of course, is the patriotic moralism that sees a simple struggle between right and wrong in international affairs, with one's own community infallibly in the right. Realism appears against this background as a skepticism concerning the relevance of moral categories to the relations among states. The realist tradition in Western thought dates to ancient Greece, particularly to the writing of the historian and political thinker Thucydides. The “classical realism” that is the subject of this chapter is a tradition that begins with Thucydides and extends through Machiavelli to the early social contract theorists Hobbes, Spinoza, and Rousseau. Though this tradition has been immensely powerful, it is to some extent an artificial construct – these thinkers did not by and large think of themselves as adherents to a tradition, but as innovators. Nevertheless, as we shall see, they share a fundamental perspective that puts them on the same side of the important questions of ethics and international politics.

The essence of international realism is its belief in the primacy of self-interest over moral principle, of necessity and therefore as of right, in international politics.