The text is considered a classic in international relations theory, and is often dubbed one of the first modern realist texts, following in the fashion of Thucydides, Machiavelli and Hobbes. Carr's analysis begins with the optimism that followed World War I, as embodied in the League of Nations declarations and various international treaties aimed at the permanent prevention of military conflict. He proceeds to demonstrate how rational, well-conceived ideas of peace and cooperation among states were undermined in short order by the realities of chaos and insecurity in the international realm. By assessing the military, economic, ideological, and juridical facets and applications of power, Carr brings harsh criticism to bear on utopian theorists who forget to consider the exigencies of survival and competition.
Carr does not, however, consider the prospect of human improvement a lost cause. At the end of The Twenty Years' Crisis, he actually advocates for the role of morality in international politics, and suggests that unmitigated Realism amounts to a dismal defeatism which we can ill afford. The sine qua non of his analysis is simply that in the conduct of international affairs, the relative balance of power must be acknowledged as a starting point.
He concludes his discussion by suggesting that "elegant superstructures" such as the League of Nations "must wait until some progress has been made in digging the foundations".