Dangerous Alliances: Proponents of Peace, Weapons of War. By Patricia A. Weitsman. Stanford: Stanford University Press, 2004. 264 pp., $49.50 (ISBN: 0-8047-4866-7). Patricia Weitsman's Dangerous Alliances begins with an oft-neglected insight about the nature of alliances. Alliances are often not just, and sometimes even not primarily, a means of aggregating power to balance the members' common foreign threats. They may be designed in the first place as devices to manage conflict among the members: to control an adversary by enmeshing it in an institution that is mutually constraining. An alliance motivated by this “tethering” imperative, to use Weitsman's term, is oriented more internally than externally. Not surprisingly, such alliances are not terribly cohesive because the internal threat often exceeds the external threat. Dangerous Alliances identifies several motivations for alliance formation and elucidates the consequences of each for alliance cohesion. But the book's distinctive contribution lies in its discussion, not of balancing or bandwagoning (terms that have long been part of the international relations lexicon), but of “tethering.” Dangerous Alliances serves as an important corrective to the conventional realist wisdom about alliances. Whether alliances are conceived as tools to balance power (Waltz 1979) or threat (Walt 1987), structural realists have agreed that they are primarily motivated by forces external to the alliance. Thus realists do not assume that allies share a wide range of interests beyond the specific casus foederis . Casting alliances as marriages of convenience, they in fact presume that the alliance “halo” is quite limited (Snyder 1997). Nonetheless, they do assume that allies share a common interest at least in balancing a rising foreign power that is perceived as a threat. As Weitsman's study of alliances among Europe's great powers between 1873 and 1918 makes abundantly clear, however, that assumption is not warranted on historical grounds. Weitsman portrays her theoretical approach as drawing in equal parts on realist and …