When do states (decision makers and their publics) rethink their world? Why and how does this happen? Change in ideas, shifts in paradigms, the overthrow of ruling ideologies have long been the focus of various theoretical perspectives. Here these questions are framed and analyzed through constructivist lenses.

Jeffrey Legro looks at the role of collective ideas in encouraging and restraining change in foreign policy, specifically whether the orientation of states is toward integration with the world and its prevailing order, separatism (isolationism), or revision of the status quo. His book builds on Judith Goldstein and Robert O. Keohane's Ideas and Foreign Policy but takes a more constructivist perspective. His aim is to show that the collective foreign policy ideas for any period are important—not by demonstrating that they “trump” other variables, like “power or interest groups” (p. 13), but that they interact with them to form “a structure within which individual and group decision making takes place” (p. 22). For Legro, the dominant ideas of a period form an ideational structure in which foreign policy is made and transformed. Radical policy change is not likely to take place without a prior change in the dominant ideas.

The first question the author asks is what makes for a change in ideas. Here, he posits that it is usually some external shock, typically associated with dramatic failure, that leads to a questioning of ideas and potentially to their collapse. The prevailing ideas will not be replaced, however, unless there is some alternative set of ideas in the wings that can take over. To understand change one must understand both the collapse of “old thinking” and the consolidation of “new thinking.”

Such a framework enables Legro to move away from solely arguing that ideas are important and move toward studying ideas in their own right. In more behavioral language, ideational change becomes a legitimate dependent variable worthy of its own analysis. He is at his best in delineating the factors that bring about collapse and consolidation. The psychological literature has long seen success and failure as key variables, and Legro draws on these—arguing that a stark failure of the old ideas to fulfill expectations, coupled with an early success of the new thinking, are most apt to bring about a shift in collective ideas. Scholars will find his categorization of the various scenarios particularly insightful (see pp. 33–38).

Although the focus is on fundamental orientations in foreign policy, the framework seems relevant to any shift in ideas, including shifts in paradigms or research programs. Indeed, those working on intellectual history will find Legro's framework more precise and informative than existing frameworks, like Thomas Kuhn's, which simply talks about paradigm displacement without really specifying the conditions that encourage displacement. An even more relevant area is the analysis of prevailing ideology. Other than a quote from Marx early in the book on the limits of man making his own history, Legro does not really engage this literature. One would like to have known what he thinks of Marx and Engels' The German Ideology and Karl Mannheim's Ideology and Utopia.

Instead, Legro focuses on realism, a not surprising choice given the debates within international relations. His comments on John Mearsheimer's offensive realism are particularly telling, showing that contrary to expectations, the United States failed to balance against a hegemonic move in 1930s Europe and waited for a German declaration of war (pp. 72–74). For the author, it is not the polarity of the system that explains U.S. behavior but shifts in U.S. attitudes (ideas). The United States did not balance when it was supposed to because the dominant ideas in the country in the 1930s were not realist, but isolationist. This ideational structure constrained even the shrewd Franklin Roosevelt, who was both a lion and a fox, from going to war with Hitler until there was an external shock. According to Legro, collective ideas can prevent states from reacting, in a timely manner, to their strategic circumstances (p. 44). It seems that realist balancing will only work well when leaders and publics follow realist ideas and construct their world around it. Those constructions themselves do not just arise automatically from materialist conditions. This is an ironic twist that constructivists will enjoy and realists will need to answer.

The heart of the book consists of four case studies that test and elaborate the theoretical claims. In the case studies, Legro wants to determine whether collective ideas play an intervening role in foreign policy change or whether that change can be explained by relying solely on the external shift in power (or threat) and/or the influence of interest groups.

The chapter on the United States makes a persuasive case for the way in which collective ideas were crucial in the shift from isolationism to internationalism. An especially nice feature is the content analysis of all State of the Union addresses from 1908 through 1950. Despite this quantitative analysis, Legro does not really mine the behavior work on American foreign policy, such as the research on the mood theory or on critical foreign policy issues.

The chapter on Germany nicely shows how ideas make for continuity from the Kaiserreich through the Weimar Republic and to the early part of Hitler's reign. Each case study illustrates the need for new ideas to be consolidated to effect change. Legro also argues that it is not just the individual (for instance, Mikhail Gorbachev) who is crucial; it is collective ideas that are a key factor in the reorientation of foreign policy, although claiming that any Soviet reform leader in 1985 would eventually have made the same decision may be going a bit too far (p. 155). Nevertheless, the cases provide impressive evidence for the importance of ideational structure. Foreign policy change is not a function of just external strategic considerations or internal domestic interests.

Rethinking the World is an original and important contribution to the ideational research program that advances our knowledge about collective ideas and foreign policy change. It deserves serious and wide attention.