Several leading international relations theories argue that the degree of interest similarity is an important determinant of dyadic conflict and cooperation. Empirical scholarshave long wrestled with operationalizing and measuring this central, yet elusive, concept. Signorino and Ritter's (1999) S algorithm, combined with multiple data sources, provides an attractive solution to this problem. To date, however, many scholars have failed to take full advantage of this solution. In this research note we examine the properties of S via simulation and with real data sources, highlighting its virtues and potential limitations. In particular, we stress the need to include multiple data sources in the computation and provide scholars with an easy-to-use tool to greatly simplify this task.Keywords interstate dyads, interest similarity, preference similarity, Scompute Signorino and Ritter (1999) propose a methodology for calculating the similarity of two column vectors, S, which has the potential to fundamentally change the way scholars of international relations (IR) measure the key concept of dyadic interest similarity. 1 Not only is S intuitively appealing, but it allows for various weighting schemes and the easy combination of multiple variables. These features should make S attractive to IR scholars on a theoretical level. To date, however, examination and use of the new method has been limited. Many studies continue to employ other algorithms, and others, while using S, fail to take full advantage of the method. In this research note we examine the properties of S,

Despite an impressive collection of classical works on the subject, little is known about the frequency or characteristics of Great Power alliance decisions to balance with the weak or bandwagon with the strong. Most works hold that balancing is the predominant Great Power alliance formation behavior, but many examples to the contrary come to mind. We clearly operationalize the concepts of balancing and bandwagoning and find that Great Powers ally with the stronger of two choices (i.e., bandwagon) more often than balance of power theory expects. We argue this surprising finding occurs because Great Powers ally based on interests, not power. We test the generalizability of our argument with a censored probit model of Great Power alliance formation on all Great Powers from 1816 to 1992.

Despite substantial evidence that international trade has promoted peace in the post—World War II era, the commercial peace research program still faces an important historical challenge. Dramatic economic integration in the nineteenth century failed to prevent the increasing interstate hostilities that culminated in the outbreak of war in 1914. This article uses a theoretical revision grounded in standard trade theory to reexamine the relationship between commerce and peace in the fifty years before World War I, a period often referred to as the first era of globalization. The article focuses on domestic conflict over commercial policy rather than on interdependence to understand the conditions under which globalization promotes peace. In a sample dating from 1865 to 1914, the authors find that lower regulatory barriers to commerce reduce participation in militarized interstate disputes. Contradicting conventional wisdom, this evidence affirms a basic premise of commercial liberalism during the first era of globalization—free trade promotes peace.

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Two fundamentalar guments are presented to answer whether dyadic balances or preponderances of military capability are more peaceful. First, the impact of the dyadic balance of military capabilities on interstate conflict, conditional on the level of dyadic interest similarity, is assessed. Many theoreticalworks in the field argue that the degree of interest similarity gives meaning to the balance of military forces, yet few empirical studies investigate the conditionality of these two variables. The second argument is that interstate conflict is a heterogeneous outcome. Aselection model that seeks to explain the severity of interstate disputes is used to address this concern. Using data from all interstate dyads between 1886 and 1992, results show that dyads with similar interests have less severe disputes, and under the condition of interest dissimilarity, balances rather than preponderances of military capability are associated with less severe disputes.