Patricia Weitsman sets out to provide a unified theory of alliance politics that explains when states will manage threatening neighbors by allying with them rather than allying against them, when allies will undertake different types of military obligations, when alliances will be more or less cohesive, and how alliances aimed at preserving peace sometimes provoke war. Although she is not entirely successful in fulfilling this extensive agenda, Dangerous Alliances is nevertheless a constructive contribution to several ongoing debates about alliance politics.

With a tip of the hat to Stephen Walt's The Origins of Alliances (1987), Weitsman accepts the idea that states form alliances in response to threats. She builds upon Walt's argument, however, by characterizing “threat” as a continuous variable and arguing that alliance behavior may vary in response to different levels of threat. Low-level threats encourage “hedging” behavior, an unspecified mix of half-hearted gestures toward both friends and enemies, aimed at preserving flexibility and forestalling trouble. Moderate threats prompt states to form “tethering” alliances with their enemies in hopes of restraining them. States form the balancing alliances described by Walt at higher levels of threat, resorting to traditional “bandwagoning” alliances only when threats become so overwhelming that balancing is impractical.

Weitsman further argues that the type of military obligations incorporated into alliance agreements and the overall cohesiveness of alliances are both a function of the character of the threat to which the allies are responding. For example, “balancing” alliances provoked by severe external threats tend to be cohesive and to involve promises of military assistance, while tethering alliances occasioned by moderate threats by alliance partners tend to be less cohesive and to involve promises of consultation or neutrality. Finally, Weitsman appeals to the security dilemma by suggesting that tethering alliances may provoke hostile reactions from nonmembers, who misunderstand the allies' aims. Although this argument seems to have provided the title for the book, it actually appears as something of an afterthought.

The most striking contribution of the book is the author's effort to sketch the underlying logic of “alliances of restraint” of the sort outlined by Paul Schroeder (see Schroeder, “Alliances 1815–1945: Weapons of Power and Tools of Management,” in Klaus Knorr, ed., Historical Dimensions of National Security Problems, 1976). An alliance can provide influence over a partner to the extent that it provides a valuable and retractable advantage relative to some third party. I have some misgivings that distinguishing tethering from balancing alliances may tend to obscure the fact that deterrent and offensive alliances also involve compromises between allies in order to secure advantages relative to third parties, but Weitsman is certainly correct that intra-alliance advantages may sometimes be the primary motive, rather than a secondary motive, for states entering into military agreements. On occasion, she argues that tethering alliances keep the peace between allies without providing any advantages against nonmembers, but unfortunately, she does not specify how such alliances provide the partners with any incentives to accommodate each other that did not exist in the absence of the alliance.

The author's ambitious argument about how states' motives translate into the types of promises they make and the reliability of the resulting alliances is perhaps a little too straightforward, omitting any role for strategic behavior or for uncertainty about the true motivations of one's partners or one's enemies. For example, she reasons that because tethered allies are wary of each other, they will promise each other only very limited support, and they are unlikely to honor even these promises if put to the test. If so, then it is not clear why such alliances provide the partners with leverage to restrain each other in the first place: Why would a potential enemy mind its manners in order to preserve a predictably worthless promise?

The major portion of the book is devoted to case studies of the major alliances between the European powers between the Congress of Berlin and the end of the First World War: the two Leagues of the Three Emperors, the Austro-German alliance, the Triple Alliance, the Franco-Russian Alliance, and the Triple Entente. This choice of cases seems a bit unfortunate, because Schroeder covers the same ground in the essay that Weitsman credits with inspiring her hypotheses on tethering alliances in the first place. Weitsman devotes a chapter to the two Leagues of the Three Emperors, which Schroeder ignored, and she rightly treats the Triple Alliance as distinct from the Austro-German alliance rather than subsidiary to it, but the reader might be forgiven a sense of déjà vu at many of her conclusions.

The case studies are well worth reading, and the author deserves credit for doing original archival research rather than relying entirely upon secondary sources. Students of the period will, of course, find points of interpretation to dispute. The studies of the second League of the Three Emperors and the Triple Alliance seem a bit unbalanced without any discussion of the Mediterranean Agreements or of Italy's dealings with France in the early 1900s. It seems to me that Weitsman underplays Austria-Hungary's ambitions to create a sort of continental coalition against Russia in favor of emphasizing its tethering motives. Her decision to follow the Triple Alliance and the Triple Entente through 1918, however, is a nice touch that sets her book apart from the crowd of studies that considers alliances only in the context of extended deterrence.

Weitsman's effort to consider alliances of mutual restraint in a “balance of threat” context is both welcome and long overdue, and her suggestion that states may adopt different alliance policies in response to different levels of threat is worthy of further consideration. Dangerous Alliances pushes Walt's balance-of-threat framework in a significant new direction, and it deserves the attention of any serious student of alliance politics.