Originating in a debate on political realism with the late Hans Morgenthau, this article purports to reanalyze some basic concepts underlying traditional realism (such as power, security, national interest, international systems) in the light of the fundamental changes in international relations that are indicated by the terms population pressure, resources depletion, environmental destruction, and, last but not least, armament races and nuclear superarmament. In suggesting solutions (an attitude and policy of universalism replacing national and other group parochialism, for instance), I have tried to keep my approach equidistant from a utopianism that would substitute world authority for the nation-state system and from a superrealism that denies the feasibility of any more internationalist policy altogether.