Realists argue that state behavior is predicated on the distribution of power in the international system. Specifically, states attempt to acquire, maintain, exercise, and balance power in response to the same behavior expected of other states in the system. In this book, Mark L. Haas offers a compelling argument for thinking beyond power variables and considering the independent effects of ideology on leaders' foreign policy decisions. The main thrust of his thesis is that the greater the ideological distance between decision makers of different states, the greater the likelihood that they will view each other as threats to domestic power and international security. Conversely, the greater the ideological affinity between states' leaders, the greater the likelihood that they will see each other as mutually supportive of one another's interests and, therefore, as less threatening. Decision makers' conflictual or accommodative foreign policies, then, are a function of threat perception caused by ideological distance. The book begins with the explication of the theoretical argument and then applies the theory to five different historical case studies. Haas concludes with policy implications and prescriptions for current and future international politics generally, and U.S. foreign policy specifically.

Haas identifies three causal mechanisms that link ideological differences among state leaders with threat perception and subsequent foreign policy choices: 1) the demonstration-effects mechanism, 2) the conflict-probability mechanism, and 3) the communications mechanism. The demonstration-effects mechanism states that leaders witness changes occurring in other states and that the increasing ideological distance induces a fear of subversion within the domestic polity. The conflict-probability mechanism is grounded in social identity theory and posits that conflict is more likely when leaders identify ideological outgroups in other states that may pose a threat to their international security. The communications mechanism asserts that ideological rivals are prone to miscommunication and misperception, thereby increasing the likelihood of conflict.

For Haas, it follows that the “degree of ideological similarities among leaders across states” is an important independent variable (p. 31). Ideological beliefs of decision makers are defined in terms of their primary economic, domestic, political, and social goals. These conceptual variables are operationalized by examining regime types, political economy systems, and the extent of civil rights. The dependent variable is the leaders' perceptions of threat and the resultant foreign policy strategies, for example, alliances, threats or use of force, defense spending, and so on. Since the author is testing his hypotheses with case studies, he uses process-tracing techniques focused on the public and private statements of leaders, as well as their actual behaviors.

Haas offers an interesting selection of historical cases spanning two hundred years: the three wars of the French Revolution, the Concert of Europe, the 1930s and the origins of World War II, the rise and fall of the Sino-Soviet alliance, and the 1980s and the end of the Cold War. While all of the cases are noteworthy, I believe that the Sino-Soviet split case study provides the strongest evidence in support of the ideological distance hypothesis. The People's Republic of China (PRC) and the USSR were ideological allies and “should” have remained so, especially in light of their shared enmity of the United States. However, Haas deftly illustrates how Mao's increasing ideological radicalization alienated the Soviet Union, even though realist arguments would predict that the two states should have allied to balance the power of the United States.

A marked strength of this book is that it does not attempt to oversell the importance of the central tenet of ideological distance. Haas does not ignore significant realist arguments, and his theoretical exposition outlines the conditions under which power variables versus ideological distance considerations would be expected to operate. The case studies bear this out as well. For example, in the chapter on the origins of World War II, he states that realist explanations based on power maximization help explain much of Soviet behavior toward Germany. Of course, he later qualifies these realist arguments and clarifies how ideological variables may have been the motivating factor behind Soviet foreign policies.

Although the book has few weaknesses, a few are worth discussing. In my view, Haas's theory of a “communications mechanism” is problematic. It posits that ideological distance will lead to miscommunication and misperception. Yet, throughout the book, he explains in great detail how leaders began to see each other as threats because of the things they said and did in terms of ideology. He admits the indeterminacy of this factor when he states that “there is not an inevitable connection between an inability to communicate effectively and increasing perceptions of international threats” (p. 14).

Second, in several places, Haas refers to the fact that power variables were constant or identical, inferring that leaders' decisions had to be based on other factors, that is, ideological variables. However, it seems plausible that different actors within and between states will have different perceptions of relative power. In such cases, power variables may play a more influential role in foreign policy decisions than otherwise accounted for by his ideological-distance thesis.

Third, I found myself repeatedly thinking of possible counterfactuals to Haas's primary thesis. For example, how do we reconcile the United States (and other Western powers) allying with the Soviet Union during World War II against Hitler's Germany when the United States had been at “ideological war” with communism long before Hitler's fascism/Nazism? Why did the PRC move toward rapprochement with the United States in the early 1970s when, ideologically speaking, Chinese leaders had much more in common with Soviet leaders, notwithstanding their disagreements? I suspect that Haas would answer that in these cases, power considerations became paramount.

Despite these weaknesses, The Ideological Origins of Great Power Politics, 1789–1989, is a definite must read. Haas is an effective writer; each of the case studies is meticulously researched, and the evidence marshaled in support of the hypotheses is impressive. The theoretical argument also lends itself nicely to what I hope will be a quantitative approach in future work. Overall, he makes a strong case for the inclusion of ideological factors, specifically distance, in examining and predicting the behavior of leaders of nation-states toward each other.