A lucid account of the forces that pushed the superpowers toward detente in the early 1970s. Not a conventional diplomatic history but a series of reflective essays, it concisely analyzes the breakdown of old arrangements in both countries and the emergence of tectonic pressures impelling Nixon and Brezhnev, with a certain degree of mutual astonishment, toward limited cooperation with each other. Nelson, a professor of history at the University of California at Irvine, has a good feel for the cyclical rhythms in international politics, and he formulates his propositions in terms readily accessible to theorists of international change. (There is also an excellent bibliographical essay in the back.) One leaves this fine book, however, with the impression that the author should have analyzed the ebbing of detente with the same care as he analyzed the flow; the strength of the waves then crashing on the heads of Soviet and American leaders cannot be justly estimated without measuring the power of the subsequent undertow.